diff options
Diffstat (limited to 'src/include/access/skey.h')
| -rw-r--r-- | src/include/access/skey.h | 35 |
1 files changed, 34 insertions, 1 deletions
diff --git a/src/include/access/skey.h b/src/include/access/skey.h index f3845e55184..ecca1b84cff 100644 --- a/src/include/access/skey.h +++ b/src/include/access/skey.h @@ -7,7 +7,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/include/access/skey.h,v 1.30 2006/01/14 22:03:35 tgl Exp $ + * $PostgreSQL: pgsql/src/include/access/skey.h,v 1.31 2006/01/25 20:29:24 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -70,6 +70,36 @@ typedef struct ScanKeyData typedef ScanKeyData *ScanKey; /* + * About row comparisons: + * + * The ScanKey data structure also supports row comparisons, that is ordered + * tuple comparisons like (x, y) > (c1, c2), having the SQL-spec semantics + * "x > c1 OR (x = c1 AND y > c2)". Note that this is currently only + * implemented for btree index searches, not for heapscans or any other index + * type. A row comparison is represented by a "header" ScanKey entry plus + * a separate array of ScanKeys, one for each column of the row comparison. + * The header entry has these properties: + * sk_flags = SK_ROW_HEADER + * sk_attno = index column number for leading column of row comparison + * sk_strategy = btree strategy code for semantics of row comparison + * (ie, < <= > or >=) + * sk_subtype, sk_func: not used + * sk_argument: pointer to subsidiary ScanKey array + * If the header is part of a ScanKey array that's sorted by attno, it + * must be sorted according to the leading column number. + * + * The subsidiary ScanKey array appears in logical column order of the row + * comparison, which may be different from index column order. The array + * elements are like a normal ScanKey array except that: + * sk_flags must include SK_ROW_MEMBER, plus SK_ROW_END in the last + * element (needed since row header does not include a count) + * sk_func points to the btree comparison support function for the + * opclass, NOT the operator's implementation function. + * sk_strategy must be the same in all elements of the subsidiary array, + * that is, the same as in the header entry. + */ + +/* * ScanKeyData sk_flags * * sk_flags bits 0-15 are reserved for system-wide use (symbols for those @@ -78,6 +108,9 @@ typedef ScanKeyData *ScanKey; */ #define SK_ISNULL 0x0001 /* sk_argument is NULL */ #define SK_UNARY 0x0002 /* unary operator (currently unsupported) */ +#define SK_ROW_HEADER 0x0004 /* row comparison header (see above) */ +#define SK_ROW_MEMBER 0x0008 /* row comparison member (see above) */ +#define SK_ROW_END 0x0010 /* last row comparison member (see above) */ /* |