diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/executor/execAmi.c | 5 | ||||
| -rw-r--r-- | src/backend/executor/nodeUnique.c | 27 |
2 files changed, 15 insertions, 17 deletions
diff --git a/src/backend/executor/execAmi.c b/src/backend/executor/execAmi.c index 154301a67f9..1381a4a4f09 100644 --- a/src/backend/executor/execAmi.c +++ b/src/backend/executor/execAmi.c @@ -6,7 +6,7 @@ * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.96 2008/07/26 19:15:35 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.97 2008/08/05 21:28:29 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -414,9 +414,6 @@ ExecSupportsBackwardScan(Plan *node) case T_Sort: return true; - case T_Unique: - return ExecSupportsBackwardScan(outerPlan(node)); - case T_Limit: return ExecSupportsBackwardScan(outerPlan(node)); diff --git a/src/backend/executor/nodeUnique.c b/src/backend/executor/nodeUnique.c index 545ba848d6a..90eb7eeef01 100644 --- a/src/backend/executor/nodeUnique.c +++ b/src/backend/executor/nodeUnique.c @@ -3,19 +3,27 @@ * nodeUnique.c * Routines to handle unique'ing of queries where appropriate * + * Unique is a very simple node type that just filters out duplicate + * tuples from a stream of sorted tuples from its subplan. It's essentially + * a dumbed-down form of Group: the duplicate-removal functionality is + * identical. However, Unique doesn't do projection nor qual checking, + * so it's marginally more efficient for cases where neither is needed. + * (It's debatable whether the savings justifies carrying two plan node + * types, though.) + * * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/executor/nodeUnique.c,v 1.56 2008/01/01 19:45:49 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/executor/nodeUnique.c,v 1.57 2008/08/05 21:28:29 tgl Exp $ * *------------------------------------------------------------------------- */ /* * INTERFACE ROUTINES * ExecUnique - generate a unique'd temporary relation - * ExecInitUnique - initialize node and subnodes.. + * ExecInitUnique - initialize node and subnodes * ExecEndUnique - shutdown node and subnodes * * NOTES @@ -32,9 +40,6 @@ /* ---------------------------------------------------------------- * ExecUnique - * - * This is a very simple node which filters out duplicate - * tuples from a stream of sorted tuples from a subplan. * ---------------------------------------------------------------- */ TupleTableSlot * /* return: a tuple or NULL */ @@ -54,11 +59,7 @@ ExecUnique(UniqueState *node) /* * now loop, returning only non-duplicate tuples. We assume that the * tuples arrive in sorted order so we can detect duplicates easily. - * - * We return the first tuple from each group of duplicates (or the last - * tuple of each group, when moving backwards). At either end of the - * subplan, clear the result slot so that we correctly return the - * first/last tuple when reversing direction. + * The first tuple of each group is returned. */ for (;;) { @@ -68,13 +69,13 @@ ExecUnique(UniqueState *node) slot = ExecProcNode(outerPlan); if (TupIsNull(slot)) { - /* end of subplan; reset in case we change direction */ + /* end of subplan, so we're done */ ExecClearTuple(resultTupleSlot); return NULL; } /* - * Always return the first/last tuple from the subplan. + * Always return the first tuple from the subplan. */ if (TupIsNull(resultTupleSlot)) break; @@ -113,7 +114,7 @@ ExecInitUnique(Unique *node, EState *estate, int eflags) UniqueState *uniquestate; /* check for unsupported flags */ - Assert(!(eflags & EXEC_FLAG_MARK)); + Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK))); /* * create state structure |