Redesign DISTINCT ON as discussed in pgsql-sql 1/25/00: syntax is now

SELECT DISTINCT ON (expr [, expr ...]) targetlist ...
and there is a check to make sure that the user didn't specify an ORDER BY
that's incompatible with the DISTINCT operation.
Reimplement nodeUnique and nodeGroup to use the proper datatype-specific
equality function for each column being compared --- they used to do
bitwise comparisons or convert the data to text strings and strcmp().
(To add insult to injury, they'd look up the conversion functions once
for each tuple...)  Parse/plan representation of DISTINCT is now a list
of SortClause nodes.
initdb forced by querytree change...

1 files changed, 15 insertions, 5 deletions

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 1346ac8a04e..288e7f96b8d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.96 2000/01/26 05:58:16 momjian Exp $
+ * $Id: parsenodes.h,v 1.97 2000/01/27 18:11:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -54,7 +54,8 @@ typedef struct Query
 	Node	   *qual;			/* qualifications applied to tuples */
 	List	   *rowMark;		/* list of RowMark entries */
 
-	char	   *uniqueFlag;		/* NULL, '*', or Unique attribute name */
+	List	   *distinctClause;	/* a list of SortClause's */
+
 	List	   *sortClause;		/* a list of SortClause's */
 
 	List	   *groupClause;	/* a list of GroupClause's */
@@ -733,7 +734,8 @@ typedef struct InsertStmt
 {
 	NodeTag		type;
 	char	   *relname;		/* relation to insert into */
-	char	   *unique;			/* NULL, '*', or unique attribute name */
+	List	   *distinctClause;	/* NULL, list of DISTINCT ON exprs, or
+								 * lcons(NIL,NIL) for all (SELECT DISTINCT) */
 	List	   *cols;			/* names of the columns */
 	List	   *targetList;		/* the target list (of ResTarget) */
 	List	   *fromClause;		/* the from clause */
@@ -777,7 +779,8 @@ typedef struct UpdateStmt
 typedef struct SelectStmt
 {
 	NodeTag		type;
-	char	   *unique;			/* NULL, '*', or unique attribute name */
+	List	   *distinctClause;	/* NULL, list of DISTINCT ON exprs, or
+								 * lcons(NIL,NIL) for all (SELECT DISTINCT) */
 	char	   *into;			/* name of table (for select into table) */
 	List	   *targetList;		/* the target list (of ResTarget) */
 	List	   *fromClause;		/* the from clause */
@@ -1135,6 +1138,13 @@ typedef struct RangeTblEntry
  * tleSortGroupRef must match ressortgroupref of exactly one Resdom of the
  * associated targetlist; that is the expression to be sorted (or grouped) by.
  * sortop is the OID of the ordering operator.
+ *
+ * SortClauses are also used to identify Resdoms that we will do a "Unique"
+ * filter step on (for SELECT DISTINCT and SELECT DISTINCT ON).  The
+ * distinctClause list is simply a copy of the relevant members of the
+ * sortClause list.  Note that distinctClause can be a subset of sortClause,
+ * but cannot have members not present in sortClause; and the members that
+ * do appear must be in the same order as in sortClause.
  */
 typedef struct SortClause
 {
@@ -1148,7 +1158,7 @@ typedef struct SortClause
  *	   representation of GROUP BY clauses
  *
  * GroupClause is exactly like SortClause except for the nodetag value
- * (and it's probably not even really necessary to have two different
+ * (it's probably not even really necessary to have two different
  * nodetags...).  We have routines that operate interchangeably on both.
  */
 typedef SortClause GroupClause;