Make all comparisons done for/with statistics use the default collation.

While this will give wrong answers when estimating selectivity for a
comparison operator that's using a non-default collation, the estimation
error probably won't be large; and anyway the former approach created
estimation errors of its own by trying to use a histogram that might have
been computed with some other collation.  So we'll adopt this simplified
approach for now and perhaps improve it sometime in the future.

This patch incorporates changes from Andres Freund to make sure that
selfuncs.c passes a valid collation OID to any datatype-specific function
it calls, in case that function wants collation information.  Said OID will
now always be DEFAULT_COLLATION_OID, but at least we won't get errors.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/include/utils/selfuncs.h b/src/include/utils/selfuncs.h
index baf6d8caf8..e9913aa049 100644
--- a/src/include/utils/selfuncs.h
+++ b/src/include/utils/selfuncs.h
@@ -74,7 +74,6 @@ typedef struct VariableStatData
 	Oid			vartype;		/* exposed type of expression */
 	Oid			atttype;		/* type to pass to get_attstatsslot */
 	int32		atttypmod;		/* typmod to pass to get_attstatsslot */
-	Oid			attcollation;	/* collation of the variable */
 	bool		isunique;		/* true if matched to a unique index */
 } VariableStatData;
 
@@ -179,7 +178,7 @@ extern Selectivity rowcomparesel(PlannerInfo *root,
 			  int varRelid, JoinType jointype, SpecialJoinInfo *sjinfo);
 
 extern void mergejoinscansel(PlannerInfo *root, Node *clause,
-				 Oid opfamily, Oid collation, int strategy, bool nulls_first,
+				 Oid opfamily, int strategy, bool nulls_first,
 				 Selectivity *leftstart, Selectivity *leftend,
 				 Selectivity *rightstart, Selectivity *rightend);