third_party/sqlite/sqlite-src-3080704/src/fkey.c

   1 /*
   2 **
   3 ** The author disclaims copyright to this source code.  In place of
   4 ** a legal notice, here is a blessing:
   5 **
   6 **    May you do good and not evil.
   7 **    May you find forgiveness for yourself and forgive others.
   8 **    May you share freely, never taking more than you give.
   9 **
  10 *************************************************************************
  11 ** This file contains code used by the compiler to add foreign key
  12 ** support to compiled SQL statements.
  13 */
  14 #include "sqliteInt.h"
  15
  16 #ifndef SQLITE_OMIT_FOREIGN_KEY
  17 #ifndef SQLITE_OMIT_TRIGGER
  18
  19 /*
  20 ** Deferred and Immediate FKs
  21 ** --------------------------
  22 **
  23 ** Foreign keys in SQLite come in two flavours: deferred and immediate.
  24 ** If an immediate foreign key constraint is violated,
  25 ** SQLITE_CONSTRAINT_FOREIGNKEY is returned and the current
  26 ** statement transaction rolled back. If a
  27 ** deferred foreign key constraint is violated, no action is taken
  28 ** immediately. However if the application attempts to commit the
  29 ** transaction before fixing the constraint violation, the attempt fails.
  30 **
  31 ** Deferred constraints are implemented using a simple counter associated
  32 ** with the database handle. The counter is set to zero each time a
  33 ** database transaction is opened. Each time a statement is executed
  34 ** that causes a foreign key violation, the counter is incremented. Each
  35 ** time a statement is executed that removes an existing violation from
  36 ** the database, the counter is decremented. When the transaction is
  37 ** committed, the commit fails if the current value of the counter is
  38 ** greater than zero. This scheme has two big drawbacks:
  39 **
  40 **   * When a commit fails due to a deferred foreign key constraint,
  41 **     there is no way to tell which foreign constraint is not satisfied,
  42 **     or which row it is not satisfied for.
  43 **
  44 **   * If the database contains foreign key violations when the
  45 **     transaction is opened, this may cause the mechanism to malfunction.
  46 **
  47 ** Despite these problems, this approach is adopted as it seems simpler
  48 ** than the alternatives.
  49 **
  50 ** INSERT operations:
  51 **
  52 **   I.1) For each FK for which the table is the child table, search
  53 **        the parent table for a match. If none is found increment the
  54 **        constraint counter.
  55 **
  56 **   I.2) For each FK for which the table is the parent table,
  57 **        search the child table for rows that correspond to the new
  58 **        row in the parent table. Decrement the counter for each row
  59 **        found (as the constraint is now satisfied).
  60 **
  61 ** DELETE operations:
  62 **
  63 **   D.1) For each FK for which the table is the child table,
  64 **        search the parent table for a row that corresponds to the
  65 **        deleted row in the child table. If such a row is not found,
  66 **        decrement the counter.
  67 **
  68 **   D.2) For each FK for which the table is the parent table, search
  69 **        the child table for rows that correspond to the deleted row
  70 **        in the parent table. For each found increment the counter.
  71 **
  72 ** UPDATE operations:
  73 **
  74 **   An UPDATE command requires that all 4 steps above are taken, but only
  75 **   for FK constraints for which the affected columns are actually
  76 **   modified (values must be compared at runtime).
  77 **
  78 ** Note that I.1 and D.1 are very similar operations, as are I.2 and D.2.
  79 ** This simplifies the implementation a bit.
  80 **
  81 ** For the purposes of immediate FK constraints, the OR REPLACE conflict
  82 ** resolution is considered to delete rows before the new row is inserted.
  83 ** If a delete caused by OR REPLACE violates an FK constraint, an exception
  84 ** is thrown, even if the FK constraint would be satisfied after the new
  85 ** row is inserted.
  86 **
  87 ** Immediate constraints are usually handled similarly. The only difference
  88 ** is that the counter used is stored as part of each individual statement
  89 ** object (struct Vdbe). If, after the statement has run, its immediate
  90 ** constraint counter is greater than zero,
  91 ** it returns SQLITE_CONSTRAINT_FOREIGNKEY
  92 ** and the statement transaction is rolled back. An exception is an INSERT
  93 ** statement that inserts a single row only (no triggers). In this case,
  94 ** instead of using a counter, an exception is thrown immediately if the
  95 ** INSERT violates a foreign key constraint. This is necessary as such
  96 ** an INSERT does not open a statement transaction.
  97 **
  98 ** TODO: How should dropping a table be handled? How should renaming a
  99 ** table be handled?
 100 **
 101 **
 102 ** Query API Notes
 103 ** ---------------
 104 **
 105 ** Before coding an UPDATE or DELETE row operation, the code-generator
 106 ** for those two operations needs to know whether or not the operation
 107 ** requires any FK processing and, if so, which columns of the original
 108 ** row are required by the FK processing VDBE code (i.e. if FKs were
 109 ** implemented using triggers, which of the old.* columns would be
 110 ** accessed). No information is required by the code-generator before
 111 ** coding an INSERT operation. The functions used by the UPDATE/DELETE
 112 ** generation code to query for this information are:
 113 **
 114 **   sqlite3FkRequired() - Test to see if FK processing is required.
 115 **   sqlite3FkOldmask()  - Query for the set of required old.* columns.
 116 **
 117 **
 118 ** Externally accessible module functions
 119 ** --------------------------------------
 120 **
 121 **   sqlite3FkCheck()    - Check for foreign key violations.
 122 **   sqlite3FkActions()  - Code triggers for ON UPDATE/ON DELETE actions.
 123 **   sqlite3FkDelete()   - Delete an FKey structure.
 124 */
 125
 126 /*
 127 ** VDBE Calling Convention
 128 ** -----------------------
 129 **
 130 ** Example:
 131 **
 132 **   For the following INSERT statement:
 133 **
 134 **     CREATE TABLE t1(a, b INTEGER PRIMARY KEY, c);
 135 **     INSERT INTO t1 VALUES(1, 2, 3.1);
 136 **
 137 **   Register (x):        2    (type integer)
 138 **   Register (x+1):      1    (type integer)
 139 **   Register (x+2):      NULL (type NULL)
 140 **   Register (x+3):      3.1  (type real)
 141 */
 142
 143 /*
 144 ** A foreign key constraint requires that the key columns in the parent
 145 ** table are collectively subject to a UNIQUE or PRIMARY KEY constraint.
 146 ** Given that pParent is the parent table for foreign key constraint pFKey,
 147 ** search the schema for a unique index on the parent key columns.
 148 **
 149 ** If successful, zero is returned. If the parent key is an INTEGER PRIMARY
 150 ** KEY column, then output variable *ppIdx is set to NULL. Otherwise, *ppIdx
 151 ** is set to point to the unique index.
 152 **
 153 ** If the parent key consists of a single column (the foreign key constraint
 154 ** is not a composite foreign key), output variable *paiCol is set to NULL.
 155 ** Otherwise, it is set to point to an allocated array of size N, where
 156 ** N is the number of columns in the parent key. The first element of the
 157 ** array is the index of the child table column that is mapped by the FK
 158 ** constraint to the parent table column stored in the left-most column
 159 ** of index *ppIdx. The second element of the array is the index of the
 160 ** child table column that corresponds to the second left-most column of
 161 ** *ppIdx, and so on.
 162 **
 163 ** If the required index cannot be found, either because:
 164 **
 165 **   1) The named parent key columns do not exist, or
 166 **
 167 **   2) The named parent key columns do exist, but are not subject to a
 168 **      UNIQUE or PRIMARY KEY constraint, or
 169 **
 170 **   3) No parent key columns were provided explicitly as part of the
 171 **      foreign key definition, and the parent table does not have a
 172 **      PRIMARY KEY, or
 173 **
 174 **   4) No parent key columns were provided explicitly as part of the
 175 **      foreign key definition, and the PRIMARY KEY of the parent table
 176 **      consists of a different number of columns to the child key in
 177 **      the child table.
 178 **
 179 ** then non-zero is returned, and a "foreign key mismatch" error loaded
 180 ** into pParse. If an OOM error occurs, non-zero is returned and the
 181 ** pParse->db->mallocFailed flag is set.
 182 */
 183 int sqlite3FkLocateIndex(
 184   Parse *pParse,                  /* Parse context to store any error in */
 185   Table *pParent,                 /* Parent table of FK constraint pFKey */
 186   FKey *pFKey,                    /* Foreign key to find index for */
 187   Index **ppIdx,                  /* OUT: Unique index on parent table */
 188   int **paiCol                    /* OUT: Map of index columns in pFKey */
 189 ){
 190   Index *pIdx = 0;                    /* Value to return via *ppIdx */
 191   int *aiCol = 0;                     /* Value to return via *paiCol */
 192   int nCol = pFKey->nCol;             /* Number of columns in parent key */
 193   char *zKey = pFKey->aCol[0].zCol;   /* Name of left-most parent key column */
 194
 195   /* The caller is responsible for zeroing output parameters. */
 196   assert( ppIdx && *ppIdx==0 );
 197   assert( !paiCol || *paiCol==0 );
 198   assert( pParse );
 199
 200   /* If this is a non-composite (single column) foreign key, check if it
 201   ** maps to the INTEGER PRIMARY KEY of table pParent. If so, leave *ppIdx
 202   ** and *paiCol set to zero and return early.
 203   **
 204   ** Otherwise, for a composite foreign key (more than one column), allocate
 205   ** space for the aiCol array (returned via output parameter *paiCol).
 206   ** Non-composite foreign keys do not require the aiCol array.
 207   */
 208   if( nCol==1 ){
 209     /* The FK maps to the IPK if any of the following are true:
 210     **
 211     **   1) There is an INTEGER PRIMARY KEY column and the FK is implicitly
 212     **      mapped to the primary key of table pParent, or
 213     **   2) The FK is explicitly mapped to a column declared as INTEGER
 214     **      PRIMARY KEY.
 215     */
 216     if( pParent->iPKey>=0 ){
 217       if( !zKey ) return 0;
 218       if( !sqlite3StrICmp(pParent->aCol[pParent->iPKey].zName, zKey) ) return 0;
 219     }
 220   }else if( paiCol ){
 221     assert( nCol>1 );
 222     aiCol = (int *)sqlite3DbMallocRaw(pParse->db, nCol*sizeof(int));
 223     if( !aiCol ) return 1;
 224     *paiCol = aiCol;
 225   }
 226
 227   for(pIdx=pParent->pIndex; pIdx; pIdx=pIdx->pNext){
 228     if( pIdx->nKeyCol==nCol && IsUniqueIndex(pIdx) ){
 229       /* pIdx is a UNIQUE index (or a PRIMARY KEY) and has the right number
 230       ** of columns. If each indexed column corresponds to a foreign key
 231       ** column of pFKey, then this index is a winner.  */
 232
 233       if( zKey==0 ){
 234         /* If zKey is NULL, then this foreign key is implicitly mapped to
 235         ** the PRIMARY KEY of table pParent. The PRIMARY KEY index may be
 236         ** identified by the test.  */
 237         if( IsPrimaryKeyIndex(pIdx) ){
 238           if( aiCol ){
 239             int i;
 240             for(i=0; i<nCol; i++) aiCol[i] = pFKey->aCol[i].iFrom;
 241           }
 242           break;
 243         }
 244       }else{
 245         /* If zKey is non-NULL, then this foreign key was declared to
 246         ** map to an explicit list of columns in table pParent. Check if this
 247         ** index matches those columns. Also, check that the index uses
 248         ** the default collation sequences for each column. */
 249         int i, j;
 250         for(i=0; i<nCol; i++){
 251           i16 iCol = pIdx->aiColumn[i];     /* Index of column in parent tbl */
 252           char *zDfltColl;                  /* Def. collation for column */
 253           char *zIdxCol;                    /* Name of indexed column */
 254
 255           /* If the index uses a collation sequence that is different from
 256           ** the default collation sequence for the column, this index is
 257           ** unusable. Bail out early in this case.  */
 258           zDfltColl = pParent->aCol[iCol].zColl;
 259           if( !zDfltColl ){
 260             zDfltColl = "BINARY";
 261           }
 262           if( sqlite3StrICmp(pIdx->azColl[i], zDfltColl) ) break;
 263
 264           zIdxCol = pParent->aCol[iCol].zName;
 265           for(j=0; j<nCol; j++){
 266             if( sqlite3StrICmp(pFKey->aCol[j].zCol, zIdxCol)==0 ){
 267               if( aiCol ) aiCol[i] = pFKey->aCol[j].iFrom;
 268               break;
 269             }
 270           }
 271           if( j==nCol ) break;
 272         }
 273         if( i==nCol ) break;      /* pIdx is usable */
 274       }
 275     }
 276   }
 277
 278   if( !pIdx ){
 279     if( !pParse->disableTriggers ){
 280       sqlite3ErrorMsg(pParse,
 281            "foreign key mismatch - \"%w\" referencing \"%w\"",
 282            pFKey->pFrom->zName, pFKey->zTo);
 283     }
 284     sqlite3DbFree(pParse->db, aiCol);
 285     return 1;
 286   }
 287
 288   *ppIdx = pIdx;
 289   return 0;
 290 }
 291
 292 /*
 293 ** This function is called when a row is inserted into or deleted from the
 294 ** child table of foreign key constraint pFKey. If an SQL UPDATE is executed
 295 ** on the child table of pFKey, this function is invoked twice for each row
 296 ** affected - once to "delete" the old row, and then again to "insert" the
 297 ** new row.
 298 **
 299 ** Each time it is called, this function generates VDBE code to locate the
 300 ** row in the parent table that corresponds to the row being inserted into
 301 ** or deleted from the child table. If the parent row can be found, no
 302 ** special action is taken. Otherwise, if the parent row can *not* be
 303 ** found in the parent table:
 304 **
 305 **   Operation | FK type   | Action taken
 306 **   --------------------------------------------------------------------------
 307 **   INSERT      immediate   Increment the "immediate constraint counter".
 308 **
 309 **   DELETE      immediate   Decrement the "immediate constraint counter".
 310 **
 311 **   INSERT      deferred    Increment the "deferred constraint counter".
 312 **
 313 **   DELETE      deferred    Decrement the "deferred constraint counter".
 314 **
 315 ** These operations are identified in the comment at the top of this file
 316 ** (fkey.c) as "I.1" and "D.1".
 317 */
 318 static void fkLookupParent(
 319   Parse *pParse,        /* Parse context */
 320   int iDb,              /* Index of database housing pTab */
 321   Table *pTab,          /* Parent table of FK pFKey */
 322   Index *pIdx,          /* Unique index on parent key columns in pTab */
 323   FKey *pFKey,          /* Foreign key constraint */
 324   int *aiCol,           /* Map from parent key columns to child table columns */
 325   int regData,          /* Address of array containing child table row */
 326   int nIncr,            /* Increment constraint counter by this */
 327   int isIgnore          /* If true, pretend pTab contains all NULL values */
 328 ){
 329   int i;                                    /* Iterator variable */
 330   Vdbe *v = sqlite3GetVdbe(pParse);         /* Vdbe to add code to */
 331   int iCur = pParse->nTab - 1;              /* Cursor number to use */
 332   int iOk = sqlite3VdbeMakeLabel(v);        /* jump here if parent key found */
 333
 334   /* If nIncr is less than zero, then check at runtime if there are any
 335   ** outstanding constraints to resolve. If there are not, there is no need
 336   ** to check if deleting this row resolves any outstanding violations.
 337   **
 338   ** Check if any of the key columns in the child table row are NULL. If
 339   ** any are, then the constraint is considered satisfied. No need to
 340   ** search for a matching row in the parent table.  */
 341   if( nIncr<0 ){
 342     sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, iOk);
 343     VdbeCoverage(v);
 344   }
 345   for(i=0; i<pFKey->nCol; i++){
 346     int iReg = aiCol[i] + regData + 1;
 347     sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iOk); VdbeCoverage(v);
 348   }
 349
 350   if( isIgnore==0 ){
 351     if( pIdx==0 ){
 352       /* If pIdx is NULL, then the parent key is the INTEGER PRIMARY KEY
 353       ** column of the parent table (table pTab).  */
 354       int iMustBeInt;               /* Address of MustBeInt instruction */
 355       int regTemp = sqlite3GetTempReg(pParse);
 356
 357       /* Invoke MustBeInt to coerce the child key value to an integer (i.e.
 358       ** apply the affinity of the parent key). If this fails, then there
 359       ** is no matching parent key. Before using MustBeInt, make a copy of
 360       ** the value. Otherwise, the value inserted into the child key column
 361       ** will have INTEGER affinity applied to it, which may not be correct.  */
 362       sqlite3VdbeAddOp2(v, OP_SCopy, aiCol[0]+1+regData, regTemp);
 363       iMustBeInt = sqlite3VdbeAddOp2(v, OP_MustBeInt, regTemp, 0);
 364       VdbeCoverage(v);
 365
 366       /* If the parent table is the same as the child table, and we are about
 367       ** to increment the constraint-counter (i.e. this is an INSERT operation),
 368       ** then check if the row being inserted matches itself. If so, do not
 369       ** increment the constraint-counter.  */
 370       if( pTab==pFKey->pFrom && nIncr==1 ){
 371         sqlite3VdbeAddOp3(v, OP_Eq, regData, iOk, regTemp); VdbeCoverage(v);
 372         sqlite3VdbeChangeP5(v, SQLITE_NOTNULL);
 373       }
 374
 375       sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);
 376       sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, regTemp); VdbeCoverage(v);
 377       sqlite3VdbeAddOp2(v, OP_Goto, 0, iOk);
 378       sqlite3VdbeJumpHere(v, sqlite3VdbeCurrentAddr(v)-2);
 379       sqlite3VdbeJumpHere(v, iMustBeInt);
 380       sqlite3ReleaseTempReg(pParse, regTemp);
 381     }else{
 382       int nCol = pFKey->nCol;
 383       int regTemp = sqlite3GetTempRange(pParse, nCol);
 384       int regRec = sqlite3GetTempReg(pParse);
 385
 386       sqlite3VdbeAddOp3(v, OP_OpenRead, iCur, pIdx->tnum, iDb);
 387       sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
 388       for(i=0; i<nCol; i++){
 389         sqlite3VdbeAddOp2(v, OP_Copy, aiCol[i]+1+regData, regTemp+i);
 390       }
 391
 392       /* If the parent table is the same as the child table, and we are about
 393       ** to increment the constraint-counter (i.e. this is an INSERT operation),
 394       ** then check if the row being inserted matches itself. If so, do not
 395       ** increment the constraint-counter.
 396       **
 397       ** If any of the parent-key values are NULL, then the row cannot match
 398       ** itself. So set JUMPIFNULL to make sure we do the OP_Found if any
 399       ** of the parent-key values are NULL (at this point it is known that
 400       ** none of the child key values are).
 401       */
 402       if( pTab==pFKey->pFrom && nIncr==1 ){
 403         int iJump = sqlite3VdbeCurrentAddr(v) + nCol + 1;
 404         for(i=0; i<nCol; i++){
 405           int iChild = aiCol[i]+1+regData;
 406           int iParent = pIdx->aiColumn[i]+1+regData;
 407           assert( aiCol[i]!=pTab->iPKey );
 408           if( pIdx->aiColumn[i]==pTab->iPKey ){
 409             /* The parent key is a composite key that includes the IPK column */
 410             iParent = regData;
 411           }
 412           sqlite3VdbeAddOp3(v, OP_Ne, iChild, iJump, iParent); VdbeCoverage(v);
 413           sqlite3VdbeChangeP5(v, SQLITE_JUMPIFNULL);
 414         }
 415         sqlite3VdbeAddOp2(v, OP_Goto, 0, iOk);
 416       }
 417
 418       sqlite3VdbeAddOp4(v, OP_MakeRecord, regTemp, nCol, regRec,
 419                         sqlite3IndexAffinityStr(v,pIdx), nCol);
 420       sqlite3VdbeAddOp4Int(v, OP_Found, iCur, iOk, regRec, 0); VdbeCoverage(v);
 421
 422       sqlite3ReleaseTempReg(pParse, regRec);
 423       sqlite3ReleaseTempRange(pParse, regTemp, nCol);
 424     }
 425   }
 426
 427   if( !pFKey->isDeferred && !(pParse->db->flags & SQLITE_DeferFKs)
 428    && !pParse->pToplevel
 429    && !pParse->isMultiWrite
 430   ){
 431     /* Special case: If this is an INSERT statement that will insert exactly
 432     ** one row into the table, raise a constraint immediately instead of
 433     ** incrementing a counter. This is necessary as the VM code is being
 434     ** generated for will not open a statement transaction.  */
 435     assert( nIncr==1 );
 436     sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
 437         OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
 438   }else{
 439     if( nIncr>0 && pFKey->isDeferred==0 ){
 440       sqlite3ParseToplevel(pParse)->mayAbort = 1;
 441     }
 442     sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
 443   }
 444
 445   sqlite3VdbeResolveLabel(v, iOk);
 446   sqlite3VdbeAddOp1(v, OP_Close, iCur);
 447 }
 448
 449
 450 /*
 451 ** Return an Expr object that refers to a memory register corresponding
 452 ** to column iCol of table pTab.
 453 **
 454 ** regBase is the first of an array of register that contains the data
 455 ** for pTab.  regBase itself holds the rowid.  regBase+1 holds the first
 456 ** column.  regBase+2 holds the second column, and so forth.
 457 */
 458 static Expr *exprTableRegister(
 459   Parse *pParse,     /* Parsing and code generating context */
 460   Table *pTab,       /* The table whose content is at r[regBase]... */
 461   int regBase,       /* Contents of table pTab */
 462   i16 iCol           /* Which column of pTab is desired */
 463 ){
 464   Expr *pExpr;
 465   Column *pCol;
 466   const char *zColl;
 467   sqlite3 *db = pParse->db;
 468
 469   pExpr = sqlite3Expr(db, TK_REGISTER, 0);
 470   if( pExpr ){
 471     if( iCol>=0 && iCol!=pTab->iPKey ){
 472       pCol = &pTab->aCol[iCol];
 473       pExpr->iTable = regBase + iCol + 1;
 474       pExpr->affinity = pCol->affinity;
 475       zColl = pCol->zColl;
 476       if( zColl==0 ) zColl = db->pDfltColl->zName;
 477       pExpr = sqlite3ExprAddCollateString(pParse, pExpr, zColl);
 478     }else{
 479       pExpr->iTable = regBase;
 480       pExpr->affinity = SQLITE_AFF_INTEGER;
 481     }
 482   }
 483   return pExpr;
 484 }
 485
 486 /*
 487 ** Return an Expr object that refers to column iCol of table pTab which
 488 ** has cursor iCur.
 489 */
 490 static Expr *exprTableColumn(
 491   sqlite3 *db,      /* The database connection */
 492   Table *pTab,      /* The table whose column is desired */
 493   int iCursor,      /* The open cursor on the table */
 494   i16 iCol          /* The column that is wanted */
 495 ){
 496   Expr *pExpr = sqlite3Expr(db, TK_COLUMN, 0);
 497   if( pExpr ){
 498     pExpr->pTab = pTab;
 499     pExpr->iTable = iCursor;
 500     pExpr->iColumn = iCol;
 501   }
 502   return pExpr;
 503 }
 504
 505 /*
 506 ** This function is called to generate code executed when a row is deleted
 507 ** from the parent table of foreign key constraint pFKey and, if pFKey is
 508 ** deferred, when a row is inserted into the same table. When generating
 509 ** code for an SQL UPDATE operation, this function may be called twice -
 510 ** once to "delete" the old row and once to "insert" the new row.
 511 **
 512 ** The code generated by this function scans through the rows in the child
 513 ** table that correspond to the parent table row being deleted or inserted.
 514 ** For each child row found, one of the following actions is taken:
 515 **
 516 **   Operation | FK type   | Action taken
 517 **   --------------------------------------------------------------------------
 518 **   DELETE      immediate   Increment the "immediate constraint counter".
 519 **                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
 520 **                           throw a "FOREIGN KEY constraint failed" exception.
 521 **
 522 **   INSERT      immediate   Decrement the "immediate constraint counter".
 523 **
 524 **   DELETE      deferred    Increment the "deferred constraint counter".
 525 **                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
 526 **                           throw a "FOREIGN KEY constraint failed" exception.
 527 **
 528 **   INSERT      deferred    Decrement the "deferred constraint counter".
 529 **
 530 ** These operations are identified in the comment at the top of this file
 531 ** (fkey.c) as "I.2" and "D.2".
 532 */
 533 static void fkScanChildren(
 534   Parse *pParse,                  /* Parse context */
 535   SrcList *pSrc,                  /* The child table to be scanned */
 536   Table *pTab,                    /* The parent table */
 537   Index *pIdx,                    /* Index on parent covering the foreign key */
 538   FKey *pFKey,                    /* The foreign key linking pSrc to pTab */
 539   int *aiCol,                     /* Map from pIdx cols to child table cols */
 540   int regData,                    /* Parent row data starts here */
 541   int nIncr                       /* Amount to increment deferred counter by */
 542 ){
 543   sqlite3 *db = pParse->db;       /* Database handle */
 544   int i;                          /* Iterator variable */
 545   Expr *pWhere = 0;               /* WHERE clause to scan with */
 546   NameContext sNameContext;       /* Context used to resolve WHERE clause */
 547   WhereInfo *pWInfo;              /* Context used by sqlite3WhereXXX() */
 548   int iFkIfZero = 0;              /* Address of OP_FkIfZero */
 549   Vdbe *v = sqlite3GetVdbe(pParse);
 550
 551   assert( pIdx==0 || pIdx->pTable==pTab );
 552   assert( pIdx==0 || pIdx->nKeyCol==pFKey->nCol );
 553   assert( pIdx!=0 || pFKey->nCol==1 );
 554   assert( pIdx!=0 || HasRowid(pTab) );
 555
 556   if( nIncr<0 ){
 557     iFkIfZero = sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, 0);
 558     VdbeCoverage(v);
 559   }
 560
 561   /* Create an Expr object representing an SQL expression like:
 562   **
 563   **   <parent-key1> = <child-key1> AND <parent-key2> = <child-key2> ...
 564   **
 565   ** The collation sequence used for the comparison should be that of
 566   ** the parent key columns. The affinity of the parent key column should
 567   ** be applied to each child key value before the comparison takes place.
 568   */
 569   for(i=0; i<pFKey->nCol; i++){
 570     Expr *pLeft;                  /* Value from parent table row */
 571     Expr *pRight;                 /* Column ref to child table */
 572     Expr *pEq;                    /* Expression (pLeft = pRight) */
 573     i16 iCol;                     /* Index of column in child table */
 574     const char *zCol;             /* Name of column in child table */
 575
 576     iCol = pIdx ? pIdx->aiColumn[i] : -1;
 577     pLeft = exprTableRegister(pParse, pTab, regData, iCol);
 578     iCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
 579     assert( iCol>=0 );
 580     zCol = pFKey->pFrom->aCol[iCol].zName;
 581     pRight = sqlite3Expr(db, TK_ID, zCol);
 582     pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight, 0);
 583     pWhere = sqlite3ExprAnd(db, pWhere, pEq);
 584   }
 585
 586   /* If the child table is the same as the parent table, then add terms
 587   ** to the WHERE clause that prevent this entry from being scanned.
 588   ** The added WHERE clause terms are like this:
 589   **
 590   **     $current_rowid!=rowid
 591   **     NOT( $current_a==a AND $current_b==b AND ... )
 592   **
 593   ** The first form is used for rowid tables.  The second form is used
 594   ** for WITHOUT ROWID tables.  In the second form, the primary key is
 595   ** (a,b,...)
 596   */
 597   if( pTab==pFKey->pFrom && nIncr>0 ){
 598     Expr *pNe;                    /* Expression (pLeft != pRight) */
 599     Expr *pLeft;                  /* Value from parent table row */
 600     Expr *pRight;                 /* Column ref to child table */
 601     if( HasRowid(pTab) ){
 602       pLeft = exprTableRegister(pParse, pTab, regData, -1);
 603       pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, -1);
 604       pNe = sqlite3PExpr(pParse, TK_NE, pLeft, pRight, 0);
 605     }else{
 606       Expr *pEq, *pAll = 0;
 607       Index *pPk = sqlite3PrimaryKeyIndex(pTab);
 608       assert( pIdx!=0 );
 609       for(i=0; i<pPk->nKeyCol; i++){
 610         i16 iCol = pIdx->aiColumn[i];
 611         pLeft = exprTableRegister(pParse, pTab, regData, iCol);
 612         pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, iCol);
 613         pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight, 0);
 614         pAll = sqlite3ExprAnd(db, pAll, pEq);
 615       }
 616       pNe = sqlite3PExpr(pParse, TK_NOT, pAll, 0, 0);
 617     }
 618     pWhere = sqlite3ExprAnd(db, pWhere, pNe);
 619   }
 620
 621   /* Resolve the references in the WHERE clause. */
 622   memset(&sNameContext, 0, sizeof(NameContext));
 623   sNameContext.pSrcList = pSrc;
 624   sNameContext.pParse = pParse;
 625   sqlite3ResolveExprNames(&sNameContext, pWhere);
 626
 627   /* Create VDBE to loop through the entries in pSrc that match the WHERE
 628   ** clause. If the constraint is not deferred, throw an exception for
 629   ** each row found. Otherwise, for deferred constraints, increment the
 630   ** deferred constraint counter by nIncr for each row selected.  */
 631   pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0, 0, 0, 0);
 632   if( nIncr>0 && pFKey->isDeferred==0 ){
 633     sqlite3ParseToplevel(pParse)->mayAbort = 1;
 634   }
 635   sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
 636   if( pWInfo ){
 637     sqlite3WhereEnd(pWInfo);
 638   }
 639
 640   /* Clean up the WHERE clause constructed above. */
 641   sqlite3ExprDelete(db, pWhere);
 642   if( iFkIfZero ){
 643     sqlite3VdbeJumpHere(v, iFkIfZero);
 644   }
 645 }
 646
 647 /*
 648 ** This function returns a linked list of FKey objects (connected by
 649 ** FKey.pNextTo) holding all children of table pTab.  For example,
 650 ** given the following schema:
 651 **
 652 **   CREATE TABLE t1(a PRIMARY KEY);
 653 **   CREATE TABLE t2(b REFERENCES t1(a);
 654 **
 655 ** Calling this function with table "t1" as an argument returns a pointer
 656 ** to the FKey structure representing the foreign key constraint on table
 657 ** "t2". Calling this function with "t2" as the argument would return a
 658 ** NULL pointer (as there are no FK constraints for which t2 is the parent
 659 ** table).
 660 */
 661 FKey *sqlite3FkReferences(Table *pTab){
 662   return (FKey *)sqlite3HashFind(&pTab->pSchema->fkeyHash, pTab->zName);
 663 }
 664
 665 /*
 666 ** The second argument is a Trigger structure allocated by the
 667 ** fkActionTrigger() routine. This function deletes the Trigger structure
 668 ** and all of its sub-components.
 669 **
 670 ** The Trigger structure or any of its sub-components may be allocated from
 671 ** the lookaside buffer belonging to database handle dbMem.
 672 */
 673 static void fkTriggerDelete(sqlite3 *dbMem, Trigger *p){
 674   if( p ){
 675     TriggerStep *pStep = p->step_list;
 676     sqlite3ExprDelete(dbMem, pStep->pWhere);
 677     sqlite3ExprListDelete(dbMem, pStep->pExprList);
 678     sqlite3SelectDelete(dbMem, pStep->pSelect);
 679     sqlite3ExprDelete(dbMem, p->pWhen);
 680     sqlite3DbFree(dbMem, p);
 681   }
 682 }
 683
 684 /*
 685 ** This function is called to generate code that runs when table pTab is
 686 ** being dropped from the database. The SrcList passed as the second argument
 687 ** to this function contains a single entry guaranteed to resolve to
 688 ** table pTab.
 689 **
 690 ** Normally, no code is required. However, if either
 691 **
 692 **   (a) The table is the parent table of a FK constraint, or
 693 **   (b) The table is the child table of a deferred FK constraint and it is
 694 **       determined at runtime that there are outstanding deferred FK
 695 **       constraint violations in the database,
 696 **
 697 ** then the equivalent of "DELETE FROM <tbl>" is executed before dropping
 698 ** the table from the database. Triggers are disabled while running this
 699 ** DELETE, but foreign key actions are not.
 700 */
 701 void sqlite3FkDropTable(Parse *pParse, SrcList *pName, Table *pTab){
 702   sqlite3 *db = pParse->db;
 703   if( (db->flags&SQLITE_ForeignKeys) && !IsVirtual(pTab) && !pTab->pSelect ){
 704     int iSkip = 0;
 705     Vdbe *v = sqlite3GetVdbe(pParse);
 706
 707     assert( v );                  /* VDBE has already been allocated */
 708     if( sqlite3FkReferences(pTab)==0 ){
 709       /* Search for a deferred foreign key constraint for which this table
 710       ** is the child table. If one cannot be found, return without
 711       ** generating any VDBE code. If one can be found, then jump over
 712       ** the entire DELETE if there are no outstanding deferred constraints
 713       ** when this statement is run.  */
 714       FKey *p;
 715       for(p=pTab->pFKey; p; p=p->pNextFrom){
 716         if( p->isDeferred || (db->flags & SQLITE_DeferFKs) ) break;
 717       }
 718       if( !p ) return;
 719       iSkip = sqlite3VdbeMakeLabel(v);
 720       sqlite3VdbeAddOp2(v, OP_FkIfZero, 1, iSkip); VdbeCoverage(v);
 721     }
 722
 723     pParse->disableTriggers = 1;
 724     sqlite3DeleteFrom(pParse, sqlite3SrcListDup(db, pName, 0), 0);
 725     pParse->disableTriggers = 0;
 726
 727     /* If the DELETE has generated immediate foreign key constraint
 728     ** violations, halt the VDBE and return an error at this point, before
 729     ** any modifications to the schema are made. This is because statement
 730     ** transactions are not able to rollback schema changes.
 731     **
 732     ** If the SQLITE_DeferFKs flag is set, then this is not required, as
 733     ** the statement transaction will not be rolled back even if FK
 734     ** constraints are violated.
 735     */
 736     if( (db->flags & SQLITE_DeferFKs)==0 ){
 737       sqlite3VdbeAddOp2(v, OP_FkIfZero, 0, sqlite3VdbeCurrentAddr(v)+2);
 738       VdbeCoverage(v);
 739       sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
 740           OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
 741     }
 742
 743     if( iSkip ){
 744       sqlite3VdbeResolveLabel(v, iSkip);
 745     }
 746   }
 747 }
 748
 749
 750 /*
 751 ** The second argument points to an FKey object representing a foreign key
 752 ** for which pTab is the child table. An UPDATE statement against pTab
 753 ** is currently being processed. For each column of the table that is
 754 ** actually updated, the corresponding element in the aChange[] array
 755 ** is zero or greater (if a column is unmodified the corresponding element
 756 ** is set to -1). If the rowid column is modified by the UPDATE statement
 757 ** the bChngRowid argument is non-zero.
 758 **
 759 ** This function returns true if any of the columns that are part of the
 760 ** child key for FK constraint *p are modified.
 761 */
 762 static int fkChildIsModified(
 763   Table *pTab,                    /* Table being updated */
 764   FKey *p,                        /* Foreign key for which pTab is the child */
 765   int *aChange,                   /* Array indicating modified columns */
 766   int bChngRowid                  /* True if rowid is modified by this update */
 767 ){
 768   int i;
 769   for(i=0; i<p->nCol; i++){
 770     int iChildKey = p->aCol[i].iFrom;
 771     if( aChange[iChildKey]>=0 ) return 1;
 772     if( iChildKey==pTab->iPKey && bChngRowid ) return 1;
 773   }
 774   return 0;
 775 }
 776
 777 /*
 778 ** The second argument points to an FKey object representing a foreign key
 779 ** for which pTab is the parent table. An UPDATE statement against pTab
 780 ** is currently being processed. For each column of the table that is
 781 ** actually updated, the corresponding element in the aChange[] array
 782 ** is zero or greater (if a column is unmodified the corresponding element
 783 ** is set to -1). If the rowid column is modified by the UPDATE statement
 784 ** the bChngRowid argument is non-zero.
 785 **
 786 ** This function returns true if any of the columns that are part of the
 787 ** parent key for FK constraint *p are modified.
 788 */
 789 static int fkParentIsModified(
 790   Table *pTab,
 791   FKey *p,
 792   int *aChange,
 793   int bChngRowid
 794 ){
 795   int i;
 796   for(i=0; i<p->nCol; i++){
 797     char *zKey = p->aCol[i].zCol;
 798     int iKey;
 799     for(iKey=0; iKey<pTab->nCol; iKey++){
 800       if( aChange[iKey]>=0 || (iKey==pTab->iPKey && bChngRowid) ){
 801         Column *pCol = &pTab->aCol[iKey];
 802         if( zKey ){
 803           if( 0==sqlite3StrICmp(pCol->zName, zKey) ) return 1;
 804         }else if( pCol->colFlags & COLFLAG_PRIMKEY ){
 805           return 1;
 806         }
 807       }
 808     }
 809   }
 810   return 0;
 811 }
 812
 813 /*
 814 ** This function is called when inserting, deleting or updating a row of
 815 ** table pTab to generate VDBE code to perform foreign key constraint
 816 ** processing for the operation.
 817 **
 818 ** For a DELETE operation, parameter regOld is passed the index of the
 819 ** first register in an array of (pTab->nCol+1) registers containing the
 820 ** rowid of the row being deleted, followed by each of the column values
 821 ** of the row being deleted, from left to right. Parameter regNew is passed
 822 ** zero in this case.
 823 **
 824 ** For an INSERT operation, regOld is passed zero and regNew is passed the
 825 ** first register of an array of (pTab->nCol+1) registers containing the new
 826 ** row data.
 827 **
 828 ** For an UPDATE operation, this function is called twice. Once before
 829 ** the original record is deleted from the table using the calling convention
 830 ** described for DELETE. Then again after the original record is deleted
 831 ** but before the new record is inserted using the INSERT convention.
 832 */
 833 void sqlite3FkCheck(
 834   Parse *pParse,                  /* Parse context */
 835   Table *pTab,                    /* Row is being deleted from this table */
 836   int regOld,                     /* Previous row data is stored here */
 837   int regNew,                     /* New row data is stored here */
 838   int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
 839   int bChngRowid                  /* True if rowid is UPDATEd */
 840 ){
 841   sqlite3 *db = pParse->db;       /* Database handle */
 842   FKey *pFKey;                    /* Used to iterate through FKs */
 843   int iDb;                        /* Index of database containing pTab */
 844   const char *zDb;                /* Name of database containing pTab */
 845   int isIgnoreErrors = pParse->disableTriggers;
 846
 847   /* Exactly one of regOld and regNew should be non-zero. */
 848   assert( (regOld==0)!=(regNew==0) );
 849
 850   /* If foreign-keys are disabled, this function is a no-op. */
 851   if( (db->flags&SQLITE_ForeignKeys)==0 ) return;
 852
 853   iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
 854   zDb = db->aDb[iDb].zName;
 855
 856   /* Loop through all the foreign key constraints for which pTab is the
 857   ** child table (the table that the foreign key definition is part of).  */
 858   for(pFKey=pTab->pFKey; pFKey; pFKey=pFKey->pNextFrom){
 859     Table *pTo;                   /* Parent table of foreign key pFKey */
 860     Index *pIdx = 0;              /* Index on key columns in pTo */
 861     int *aiFree = 0;
 862     int *aiCol;
 863     int iCol;
 864     int i;
 865     int isIgnore = 0;
 866
 867     if( aChange
 868      && sqlite3_stricmp(pTab->zName, pFKey->zTo)!=0
 869      && fkChildIsModified(pTab, pFKey, aChange, bChngRowid)==0
 870     ){
 871       continue;
 872     }
 873
 874     /* Find the parent table of this foreign key. Also find a unique index
 875     ** on the parent key columns in the parent table. If either of these
 876     ** schema items cannot be located, set an error in pParse and return
 877     ** early.  */
 878     if( pParse->disableTriggers ){
 879       pTo = sqlite3FindTable(db, pFKey->zTo, zDb);
 880     }else{
 881       pTo = sqlite3LocateTable(pParse, 0, pFKey->zTo, zDb);
 882     }
 883     if( !pTo || sqlite3FkLocateIndex(pParse, pTo, pFKey, &pIdx, &aiFree) ){
 884       assert( isIgnoreErrors==0 || (regOld!=0 && regNew==0) );
 885       if( !isIgnoreErrors || db->mallocFailed ) return;
 886       if( pTo==0 ){
 887         /* If isIgnoreErrors is true, then a table is being dropped. In this
 888         ** case SQLite runs a "DELETE FROM xxx" on the table being dropped
 889         ** before actually dropping it in order to check FK constraints.
 890         ** If the parent table of an FK constraint on the current table is
 891         ** missing, behave as if it is empty. i.e. decrement the relevant
 892         ** FK counter for each row of the current table with non-NULL keys.
 893         */
 894         Vdbe *v = sqlite3GetVdbe(pParse);
 895         int iJump = sqlite3VdbeCurrentAddr(v) + pFKey->nCol + 1;
 896         for(i=0; i<pFKey->nCol; i++){
 897           int iReg = pFKey->aCol[i].iFrom + regOld + 1;
 898           sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iJump); VdbeCoverage(v);
 899         }
 900         sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, -1);
 901       }
 902       continue;
 903     }
 904     assert( pFKey->nCol==1 || (aiFree && pIdx) );
 905
 906     if( aiFree ){
 907       aiCol = aiFree;
 908     }else{
 909       iCol = pFKey->aCol[0].iFrom;
 910       aiCol = &iCol;
 911     }
 912     for(i=0; i<pFKey->nCol; i++){
 913       if( aiCol[i]==pTab->iPKey ){
 914         aiCol[i] = -1;
 915       }
 916 #ifndef SQLITE_OMIT_AUTHORIZATION
 917       /* Request permission to read the parent key columns. If the
 918       ** authorization callback returns SQLITE_IGNORE, behave as if any
 919       ** values read from the parent table are NULL. */
 920       if( db->xAuth ){
 921         int rcauth;
 922         char *zCol = pTo->aCol[pIdx ? pIdx->aiColumn[i] : pTo->iPKey].zName;
 923         rcauth = sqlite3AuthReadCol(pParse, pTo->zName, zCol, iDb);
 924         isIgnore = (rcauth==SQLITE_IGNORE);
 925       }
 926 #endif
 927     }
 928
 929     /* Take a shared-cache advisory read-lock on the parent table. Allocate
 930     ** a cursor to use to search the unique index on the parent key columns
 931     ** in the parent table.  */
 932     sqlite3TableLock(pParse, iDb, pTo->tnum, 0, pTo->zName);
 933     pParse->nTab++;
 934
 935     if( regOld!=0 ){
 936       /* A row is being removed from the child table. Search for the parent.
 937       ** If the parent does not exist, removing the child row resolves an
 938       ** outstanding foreign key constraint violation. */
 939       fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regOld, -1,isIgnore);
 940     }
 941     if( regNew!=0 ){
 942       /* A row is being added to the child table. If a parent row cannot
 943       ** be found, adding the child row has violated the FK constraint. */
 944       fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regNew, +1,isIgnore);
 945     }
 946
 947     sqlite3DbFree(db, aiFree);
 948   }
 949
 950   /* Loop through all the foreign key constraints that refer to this table.
 951   ** (the "child" constraints) */
 952   for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
 953     Index *pIdx = 0;              /* Foreign key index for pFKey */
 954     SrcList *pSrc;
 955     int *aiCol = 0;
 956
 957     if( aChange && fkParentIsModified(pTab, pFKey, aChange, bChngRowid)==0 ){
 958       continue;
 959     }
 960
 961     if( !pFKey->isDeferred && !(db->flags & SQLITE_DeferFKs)
 962      && !pParse->pToplevel && !pParse->isMultiWrite
 963     ){
 964       assert( regOld==0 && regNew!=0 );
 965       /* Inserting a single row into a parent table cannot cause an immediate
 966       ** foreign key violation. So do nothing in this case.  */
 967       continue;
 968     }
 969
 970     if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ){
 971       if( !isIgnoreErrors || db->mallocFailed ) return;
 972       continue;
 973     }
 974     assert( aiCol || pFKey->nCol==1 );
 975
 976     /* Create a SrcList structure containing the child table.  We need the
 977     ** child table as a SrcList for sqlite3WhereBegin() */
 978     pSrc = sqlite3SrcListAppend(db, 0, 0, 0);
 979     if( pSrc ){
 980       struct SrcList_item *pItem = pSrc->a;
 981       pItem->pTab = pFKey->pFrom;
 982       pItem->zName = pFKey->pFrom->zName;
 983       pItem->pTab->nRef++;
 984       pItem->iCursor = pParse->nTab++;
 985
 986       if( regNew!=0 ){
 987         fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regNew, -1);
 988       }
 989       if( regOld!=0 ){
 990         /* If there is a RESTRICT action configured for the current operation
 991         ** on the parent table of this FK, then throw an exception
 992         ** immediately if the FK constraint is violated, even if this is a
 993         ** deferred trigger. That's what RESTRICT means. To defer checking
 994         ** the constraint, the FK should specify NO ACTION (represented
 995         ** using OE_None). NO ACTION is the default.  */
 996         fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regOld, 1);
 997       }
 998       pItem->zName = 0;
 999       sqlite3SrcListDelete(db, pSrc);
1000     }
1001     sqlite3DbFree(db, aiCol);
1002   }
1003 }
1004
1005 #define COLUMN_MASK(x) (((x)>31) ? 0xffffffff : ((u32)1<<(x)))
1006
1007 /*
1008 ** This function is called before generating code to update or delete a
1009 ** row contained in table pTab.
1010 */
1011 u32 sqlite3FkOldmask(
1012   Parse *pParse,                  /* Parse context */
1013   Table *pTab                     /* Table being modified */
1014 ){
1015   u32 mask = 0;
1016   if( pParse->db->flags&SQLITE_ForeignKeys ){
1017     FKey *p;
1018     int i;
1019     for(p=pTab->pFKey; p; p=p->pNextFrom){
1020       for(i=0; i<p->nCol; i++) mask |= COLUMN_MASK(p->aCol[i].iFrom);
1021     }
1022     for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
1023       Index *pIdx = 0;
1024       sqlite3FkLocateIndex(pParse, pTab, p, &pIdx, 0);
1025       if( pIdx ){
1026         for(i=0; i<pIdx->nKeyCol; i++) mask |= COLUMN_MASK(pIdx->aiColumn[i]);
1027       }
1028     }
1029   }
1030   return mask;
1031 }
1032
1033
1034 /*
1035 ** This function is called before generating code to update or delete a
1036 ** row contained in table pTab. If the operation is a DELETE, then
1037 ** parameter aChange is passed a NULL value. For an UPDATE, aChange points
1038 ** to an array of size N, where N is the number of columns in table pTab.
1039 ** If the i'th column is not modified by the UPDATE, then the corresponding
1040 ** entry in the aChange[] array is set to -1. If the column is modified,
1041 ** the value is 0 or greater. Parameter chngRowid is set to true if the
1042 ** UPDATE statement modifies the rowid fields of the table.
1043 **
1044 ** If any foreign key processing will be required, this function returns
1045 ** true. If there is no foreign key related processing, this function
1046 ** returns false.
1047 */
1048 int sqlite3FkRequired(
1049   Parse *pParse,                  /* Parse context */
1050   Table *pTab,                    /* Table being modified */
1051   int *aChange,                   /* Non-NULL for UPDATE operations */
1052   int chngRowid                   /* True for UPDATE that affects rowid */
1053 ){
1054   if( pParse->db->flags&SQLITE_ForeignKeys ){
1055     if( !aChange ){
1056       /* A DELETE operation. Foreign key processing is required if the
1057       ** table in question is either the child or parent table for any
1058       ** foreign key constraint.  */
1059       return (sqlite3FkReferences(pTab) || pTab->pFKey);
1060     }else{
1061       /* This is an UPDATE. Foreign key processing is only required if the
1062       ** operation modifies one or more child or parent key columns. */
1063       FKey *p;
1064
1065       /* Check if any child key columns are being modified. */
1066       for(p=pTab->pFKey; p; p=p->pNextFrom){
1067         if( fkChildIsModified(pTab, p, aChange, chngRowid) ) return 1;
1068       }
1069
1070       /* Check if any parent key columns are being modified. */
1071       for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
1072         if( fkParentIsModified(pTab, p, aChange, chngRowid) ) return 1;
1073       }
1074     }
1075   }
1076   return 0;
1077 }
1078
1079 /*
1080 ** This function is called when an UPDATE or DELETE operation is being
1081 ** compiled on table pTab, which is the parent table of foreign-key pFKey.
1082 ** If the current operation is an UPDATE, then the pChanges parameter is
1083 ** passed a pointer to the list of columns being modified. If it is a
1084 ** DELETE, pChanges is passed a NULL pointer.
1085 **
1086 ** It returns a pointer to a Trigger structure containing a trigger
1087 ** equivalent to the ON UPDATE or ON DELETE action specified by pFKey.
1088 ** If the action is "NO ACTION" or "RESTRICT", then a NULL pointer is
1089 ** returned (these actions require no special handling by the triggers
1090 ** sub-system, code for them is created by fkScanChildren()).
1091 **
1092 ** For example, if pFKey is the foreign key and pTab is table "p" in
1093 ** the following schema:
1094 **
1095 **   CREATE TABLE p(pk PRIMARY KEY);
1096 **   CREATE TABLE c(ck REFERENCES p ON DELETE CASCADE);
1097 **
1098 ** then the returned trigger structure is equivalent to:
1099 **
1100 **   CREATE TRIGGER ... DELETE ON p BEGIN
1101 **     DELETE FROM c WHERE ck = old.pk;
1102 **   END;
1103 **
1104 ** The returned pointer is cached as part of the foreign key object. It
1105 ** is eventually freed along with the rest of the foreign key object by
1106 ** sqlite3FkDelete().
1107 */
1108 static Trigger *fkActionTrigger(
1109   Parse *pParse,                  /* Parse context */
1110   Table *pTab,                    /* Table being updated or deleted from */
1111   FKey *pFKey,                    /* Foreign key to get action for */
1112   ExprList *pChanges              /* Change-list for UPDATE, NULL for DELETE */
1113 ){
1114   sqlite3 *db = pParse->db;       /* Database handle */
1115   int action;                     /* One of OE_None, OE_Cascade etc. */
1116   Trigger *pTrigger;              /* Trigger definition to return */
1117   int iAction = (pChanges!=0);    /* 1 for UPDATE, 0 for DELETE */
1118
1119   action = pFKey->aAction[iAction];
1120   pTrigger = pFKey->apTrigger[iAction];
1121
1122   if( action!=OE_None && !pTrigger ){
1123     u8 enableLookaside;           /* Copy of db->lookaside.bEnabled */
1124     char const *zFrom;            /* Name of child table */
1125     int nFrom;                    /* Length in bytes of zFrom */
1126     Index *pIdx = 0;              /* Parent key index for this FK */
1127     int *aiCol = 0;               /* child table cols -> parent key cols */
1128     TriggerStep *pStep = 0;        /* First (only) step of trigger program */
1129     Expr *pWhere = 0;             /* WHERE clause of trigger step */
1130     ExprList *pList = 0;          /* Changes list if ON UPDATE CASCADE */
1131     Select *pSelect = 0;          /* If RESTRICT, "SELECT RAISE(...)" */
1132     int i;                        /* Iterator variable */
1133     Expr *pWhen = 0;              /* WHEN clause for the trigger */
1134
1135     if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ) return 0;
1136     assert( aiCol || pFKey->nCol==1 );
1137
1138     for(i=0; i<pFKey->nCol; i++){
1139       Token tOld = { "old", 3 };  /* Literal "old" token */
1140       Token tNew = { "new", 3 };  /* Literal "new" token */
1141       Token tFromCol;             /* Name of column in child table */
1142       Token tToCol;               /* Name of column in parent table */
1143       int iFromCol;               /* Idx of column in child table */
1144       Expr *pEq;                  /* tFromCol = OLD.tToCol */
1145
1146       iFromCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
1147       assert( iFromCol>=0 );
1148       tToCol.z = pIdx ? pTab->aCol[pIdx->aiColumn[i]].zName : "oid";
1149       tFromCol.z = pFKey->pFrom->aCol[iFromCol].zName;
1150
1151       tToCol.n = sqlite3Strlen30(tToCol.z);
1152       tFromCol.n = sqlite3Strlen30(tFromCol.z);
1153
1154       /* Create the expression "OLD.zToCol = zFromCol". It is important
1155       ** that the "OLD.zToCol" term is on the LHS of the = operator, so
1156       ** that the affinity and collation sequence associated with the
1157       ** parent table are used for the comparison. */
1158       pEq = sqlite3PExpr(pParse, TK_EQ,
1159           sqlite3PExpr(pParse, TK_DOT,
1160             sqlite3PExpr(pParse, TK_ID, 0, 0, &tOld),
1161             sqlite3PExpr(pParse, TK_ID, 0, 0, &tToCol)
1162           , 0),
1163           sqlite3PExpr(pParse, TK_ID, 0, 0, &tFromCol)
1164       , 0);
1165       pWhere = sqlite3ExprAnd(db, pWhere, pEq);
1166
1167       /* For ON UPDATE, construct the next term of the WHEN clause.
1168       ** The final WHEN clause will be like this:
1169       **
1170       **    WHEN NOT(old.col1 IS new.col1 AND ... AND old.colN IS new.colN)
1171       */
1172       if( pChanges ){
1173         pEq = sqlite3PExpr(pParse, TK_IS,
1174             sqlite3PExpr(pParse, TK_DOT,
1175               sqlite3PExpr(pParse, TK_ID, 0, 0, &tOld),
1176               sqlite3PExpr(pParse, TK_ID, 0, 0, &tToCol),
1177               0),
1178             sqlite3PExpr(pParse, TK_DOT,
1179               sqlite3PExpr(pParse, TK_ID, 0, 0, &tNew),
1180               sqlite3PExpr(pParse, TK_ID, 0, 0, &tToCol),
1181               0),
1182             0);
1183         pWhen = sqlite3ExprAnd(db, pWhen, pEq);
1184       }
1185
1186       if( action!=OE_Restrict && (action!=OE_Cascade || pChanges) ){
1187         Expr *pNew;
1188         if( action==OE_Cascade ){
1189           pNew = sqlite3PExpr(pParse, TK_DOT,
1190             sqlite3PExpr(pParse, TK_ID, 0, 0, &tNew),
1191             sqlite3PExpr(pParse, TK_ID, 0, 0, &tToCol)
1192           , 0);
1193         }else if( action==OE_SetDflt ){
1194           Expr *pDflt = pFKey->pFrom->aCol[iFromCol].pDflt;
1195           if( pDflt ){
1196             pNew = sqlite3ExprDup(db, pDflt, 0);
1197           }else{
1198             pNew = sqlite3PExpr(pParse, TK_NULL, 0, 0, 0);
1199           }
1200         }else{
1201           pNew = sqlite3PExpr(pParse, TK_NULL, 0, 0, 0);
1202         }
1203         pList = sqlite3ExprListAppend(pParse, pList, pNew);
1204         sqlite3ExprListSetName(pParse, pList, &tFromCol, 0);
1205       }
1206     }
1207     sqlite3DbFree(db, aiCol);
1208
1209     zFrom = pFKey->pFrom->zName;
1210     nFrom = sqlite3Strlen30(zFrom);
1211
1212     if( action==OE_Restrict ){
1213       Token tFrom;
1214       Expr *pRaise;
1215
1216       tFrom.z = zFrom;
1217       tFrom.n = nFrom;
1218       pRaise = sqlite3Expr(db, TK_RAISE, "FOREIGN KEY constraint failed");
1219       if( pRaise ){
1220         pRaise->affinity = OE_Abort;
1221       }
1222       pSelect = sqlite3SelectNew(pParse,
1223           sqlite3ExprListAppend(pParse, 0, pRaise),
1224           sqlite3SrcListAppend(db, 0, &tFrom, 0),
1225           pWhere,
1226           0, 0, 0, 0, 0, 0
1227       );
1228       pWhere = 0;
1229     }
1230
1231     /* Disable lookaside memory allocation */
1232     enableLookaside = db->lookaside.bEnabled;
1233     db->lookaside.bEnabled = 0;
1234
1235     pTrigger = (Trigger *)sqlite3DbMallocZero(db,
1236         sizeof(Trigger) +         /* struct Trigger */
1237         sizeof(TriggerStep) +     /* Single step in trigger program */
1238         nFrom + 1                 /* Space for pStep->target.z */
1239     );
1240     if( pTrigger ){
1241       pStep = pTrigger->step_list = (TriggerStep *)&pTrigger[1];
1242       pStep->target.z = (char *)&pStep[1];
1243       pStep->target.n = nFrom;
1244       memcpy((char *)pStep->target.z, zFrom, nFrom);
1245
1246       pStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
1247       pStep->pExprList = sqlite3ExprListDup(db, pList, EXPRDUP_REDUCE);
1248       pStep->pSelect = sqlite3SelectDup(db, pSelect, EXPRDUP_REDUCE);
1249       if( pWhen ){
1250         pWhen = sqlite3PExpr(pParse, TK_NOT, pWhen, 0, 0);
1251         pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
1252       }
1253     }
1254
1255     /* Re-enable the lookaside buffer, if it was disabled earlier. */
1256     db->lookaside.bEnabled = enableLookaside;
1257
1258     sqlite3ExprDelete(db, pWhere);
1259     sqlite3ExprDelete(db, pWhen);
1260     sqlite3ExprListDelete(db, pList);
1261     sqlite3SelectDelete(db, pSelect);
1262     if( db->mallocFailed==1 ){
1263       fkTriggerDelete(db, pTrigger);
1264       return 0;
1265     }
1266     assert( pStep!=0 );
1267
1268     switch( action ){
1269       case OE_Restrict:
1270         pStep->op = TK_SELECT;
1271         break;
1272       case OE_Cascade:
1273         if( !pChanges ){
1274           pStep->op = TK_DELETE;
1275           break;
1276         }
1277       default:
1278         pStep->op = TK_UPDATE;
1279     }
1280     pStep->pTrig = pTrigger;
1281     pTrigger->pSchema = pTab->pSchema;
1282     pTrigger->pTabSchema = pTab->pSchema;
1283     pFKey->apTrigger[iAction] = pTrigger;
1284     pTrigger->op = (pChanges ? TK_UPDATE : TK_DELETE);
1285   }
1286
1287   return pTrigger;
1288 }
1289
1290 /*
1291 ** This function is called when deleting or updating a row to implement
1292 ** any required CASCADE, SET NULL or SET DEFAULT actions.
1293 */
1294 void sqlite3FkActions(
1295   Parse *pParse,                  /* Parse context */
1296   Table *pTab,                    /* Table being updated or deleted from */
1297   ExprList *pChanges,             /* Change-list for UPDATE, NULL for DELETE */
1298   int regOld,                     /* Address of array containing old row */
1299   int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
1300   int bChngRowid                  /* True if rowid is UPDATEd */
1301 ){
1302   /* If foreign-key support is enabled, iterate through all FKs that
1303   ** refer to table pTab. If there is an action associated with the FK
1304   ** for this operation (either update or delete), invoke the associated
1305   ** trigger sub-program.  */
1306   if( pParse->db->flags&SQLITE_ForeignKeys ){
1307     FKey *pFKey;                  /* Iterator variable */
1308     for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
1309       if( aChange==0 || fkParentIsModified(pTab, pFKey, aChange, bChngRowid) ){
1310         Trigger *pAct = fkActionTrigger(pParse, pTab, pFKey, pChanges);
1311         if( pAct ){
1312           sqlite3CodeRowTriggerDirect(pParse, pAct, pTab, regOld, OE_Abort, 0);
1313         }
1314       }
1315     }
1316   }
1317 }
1318
1319 #endif /* ifndef SQLITE_OMIT_TRIGGER */
1320
1321 /*
1322 ** Free all memory associated with foreign key definitions attached to
1323 ** table pTab. Remove the deleted foreign keys from the Schema.fkeyHash
1324 ** hash table.
1325 */
1326 void sqlite3FkDelete(sqlite3 *db, Table *pTab){
1327   FKey *pFKey;                    /* Iterator variable */
1328   FKey *pNext;                    /* Copy of pFKey->pNextFrom */
1329
1330   assert( db==0 || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
1331   for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
1332
1333     /* Remove the FK from the fkeyHash hash table. */
1334     if( !db || db->pnBytesFreed==0 ){
1335       if( pFKey->pPrevTo ){
1336         pFKey->pPrevTo->pNextTo = pFKey->pNextTo;
1337       }else{
1338         void *p = (void *)pFKey->pNextTo;
1339         const char *z = (p ? pFKey->pNextTo->zTo : pFKey->zTo);
1340         sqlite3HashInsert(&pTab->pSchema->fkeyHash, z, p);
1341       }
1342       if( pFKey->pNextTo ){
1343         pFKey->pNextTo->pPrevTo = pFKey->pPrevTo;
1344       }
1345     }
1346
1347     /* EV: R-30323-21917 Each foreign key constraint in SQLite is
1348     ** classified as either immediate or deferred.
1349     */
1350     assert( pFKey->isDeferred==0 || pFKey->isDeferred==1 );
1351
1352     /* Delete any triggers created to implement actions for this FK. */
1353 #ifndef SQLITE_OMIT_TRIGGER
1354     fkTriggerDelete(db, pFKey->apTrigger[0]);
1355     fkTriggerDelete(db, pFKey->apTrigger[1]);
1356 #endif
1357
1358     pNext = pFKey->pNextFrom;
1359     sqlite3DbFree(db, pFKey);
1360   }
1361 }
1362 #endif /* ifndef SQLITE_OMIT_FOREIGN_KEY */