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Teach the system how to use hashing for UNION. (INTERSECT/EXCEPT will follow,

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but seem like a separate patch since most of the remaining work is on the
executor side.)  I took the opportunity to push selection of the grouping
operators for set operations into the parser where it belongs.  Otherwise this
is just a small exercise in making prepunion.c consider both alternatives.

As with the recent DISTINCT patch, this means we can UNION on datatypes that
can hash but not sort, and it means that UNION without ORDER BY is no longer
certain to produce sorted output.
This commit is contained in:
Tom Lane
2008-08-07 01:11:52 +00:00
parent 3d40d5e70e
commit 2d1d96b1ce
20 changed files with 462 additions and 212 deletions
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11
src/include/nodes/parsenodes.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.370 2008/08/02 21:32:00 tgl Exp $
* $PostgreSQL: pgsql/src/include/nodes/parsenodes.h,v 1.371 2008/08/07 01:11:51 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -797,7 +797,12 @@ typedef struct SelectStmt
* top-level Query node containing the leaf SELECTs as subqueries in its
* range table. Its setOperations field shows the tree of set operations,
* with leaf SelectStmt nodes replaced by RangeTblRef nodes, and internal
* nodes replaced by SetOperationStmt nodes.
* nodes replaced by SetOperationStmt nodes. Information about the output
* column types is added, too. (Note that the child nodes do not necessarily
* produce these types directly, but we've checked that their output types
* can be coerced to the output column type.) Also, if it's not UNION ALL,
* information about the types' sort/group semantics is provided in the form
* of a SortGroupClause list (same representation as, eg, DISTINCT).
* ----------------------
*/
typedef struct SetOperationStmt
@@ -812,6 +817,8 @@ typedef struct SetOperationStmt
/* Fields derived during parse analysis: */
List *colTypes; /* OID list of output column type OIDs */
List *colTypmods; /* integer list of output column typmods */
List *groupClauses; /* a list of SortGroupClause's */
/* groupClauses is NIL if UNION ALL, but must be set otherwise */
} SetOperationStmt;