src/include/access/skey.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * skey.h
   4  *        POSTGRES scan key definitions.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * $PostgreSQL$
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef SKEY_H
  15 #define SKEY_H
  16
  17 #include "access/attnum.h"
  18 #include "fmgr.h"
  19
  20
  21 /*
  22  * Strategy numbers identify the semantics that particular operators have
  23  * with respect to particular operator classes.  In some cases a strategy
  24  * subtype (an OID) is used as further information.
  25  */
  26 typedef uint16 StrategyNumber;
  27
  28 #define InvalidStrategy ((StrategyNumber) 0)
  29
  30 /*
  31  * We define the strategy numbers for B-tree indexes here, to avoid having
  32  * to import access/nbtree.h into a lot of places that shouldn't need it.
  33  */
  34 #define BTLessStrategyNumber                    1
  35 #define BTLessEqualStrategyNumber               2
  36 #define BTEqualStrategyNumber                   3
  37 #define BTGreaterEqualStrategyNumber    4
  38 #define BTGreaterStrategyNumber                 5
  39
  40 #define BTMaxStrategyNumber                             5
  41
  42
  43 /*
  44  * A ScanKey represents the application of a comparison operator between
  45  * a table or index column and a constant.      When it's part of an array of
  46  * ScanKeys, the comparison conditions are implicitly ANDed.  The index
  47  * column is the left argument of the operator, if it's a binary operator.
  48  * (The data structure can support unary indexable operators too; in that
  49  * case sk_argument would go unused.  This is not currently implemented.)
  50  *
  51  * For an index scan, sk_strategy and sk_subtype must be set correctly for
  52  * the operator.  When using a ScanKey in a heap scan, these fields are not
  53  * used and may be set to InvalidStrategy/InvalidOid.
  54  *
  55  * A ScanKey can also represent a condition "column IS NULL"; this is signaled
  56  * by the SK_SEARCHNULL flag bit.  In this case the argument is always NULL,
  57  * and the sk_strategy, sk_subtype, and sk_func fields are not used (unless
  58  * set by the index AM).  Currently, SK_SEARCHNULL is supported only for
  59  * index scans, not heap scans; and not all index AMs support it.
  60  *
  61  * Note: in some places, ScanKeys are used as a convenient representation
  62  * for the invocation of an access method support procedure.  In this case
  63  * sk_strategy/sk_subtype are not meaningful, and sk_func may refer to a
  64  * function that returns something other than boolean.
  65  */
  66 typedef struct ScanKeyData
  67 {
  68         int                     sk_flags;               /* flags, see below */
  69         AttrNumber      sk_attno;               /* table or index column number */
  70         StrategyNumber sk_strategy; /* operator strategy number */
  71         Oid                     sk_subtype;             /* strategy subtype */
  72         FmgrInfo        sk_func;                /* lookup info for function to call */
  73         Datum           sk_argument;    /* data to compare */
  74 } ScanKeyData;
  75
  76 typedef ScanKeyData *ScanKey;
  77
  78 /*
  79  * About row comparisons:
  80  *
  81  * The ScanKey data structure also supports row comparisons, that is ordered
  82  * tuple comparisons like (x, y) > (c1, c2), having the SQL-spec semantics
  83  * "x > c1 OR (x = c1 AND y > c2)".  Note that this is currently only
  84  * implemented for btree index searches, not for heapscans or any other index
  85  * type.  A row comparison is represented by a "header" ScanKey entry plus
  86  * a separate array of ScanKeys, one for each column of the row comparison.
  87  * The header entry has these properties:
  88  *              sk_flags = SK_ROW_HEADER
  89  *              sk_attno = index column number for leading column of row comparison
  90  *              sk_strategy = btree strategy code for semantics of row comparison
  91  *                              (ie, < <= > or >=)
  92  *              sk_subtype, sk_func: not used
  93  *              sk_argument: pointer to subsidiary ScanKey array
  94  * If the header is part of a ScanKey array that's sorted by attno, it
  95  * must be sorted according to the leading column number.
  96  *
  97  * The subsidiary ScanKey array appears in logical column order of the row
  98  * comparison, which may be different from index column order.  The array
  99  * elements are like a normal ScanKey array except that:
 100  *              sk_flags must include SK_ROW_MEMBER, plus SK_ROW_END in the last
 101  *                              element (needed since row header does not include a count)
 102  *              sk_func points to the btree comparison support function for the
 103  *                              opclass, NOT the operator's implementation function.
 104  * sk_strategy must be the same in all elements of the subsidiary array,
 105  * that is, the same as in the header entry.
 106  */
 107
 108 /*
 109  * ScanKeyData sk_flags
 110  *
 111  * sk_flags bits 0-15 are reserved for system-wide use (symbols for those
 112  * bits should be defined here).  Bits 16-31 are reserved for use within
 113  * individual index access methods.
 114  */
 115 #define SK_ISNULL               0x0001  /* sk_argument is NULL */
 116 #define SK_UNARY                0x0002  /* unary operator (currently unsupported) */
 117 #define SK_ROW_HEADER   0x0004  /* row comparison header (see above) */
 118 #define SK_ROW_MEMBER   0x0008  /* row comparison member (see above) */
 119 #define SK_ROW_END              0x0010  /* last row comparison member (see above) */
 120 #define SK_SEARCHNULL   0x0020  /* scankey represents a "col IS NULL" qual */
 121
 122
 123 /*
 124  * prototypes for functions in access/common/scankey.c
 125  */
 126 extern void ScanKeyInit(ScanKey entry,
 127                         AttrNumber attributeNumber,
 128                         StrategyNumber strategy,
 129                         RegProcedure procedure,
 130                         Datum argument);
 131 extern void ScanKeyEntryInitialize(ScanKey entry,
 132                                            int flags,
 133                                            AttrNumber attributeNumber,
 134                                            StrategyNumber strategy,
 135                                            Oid subtype,
 136                                            RegProcedure procedure,
 137                                            Datum argument);
 138 extern void ScanKeyEntryInitializeWithInfo(ScanKey entry,
 139                                                            int flags,
 140                                                            AttrNumber attributeNumber,
 141                                                            StrategyNumber strategy,
 142                                                            Oid subtype,
 143                                                            FmgrInfo *finfo,
 144                                                            Datum argument);
 145
 146 #endif   /* SKEY_H */