4 files changed, 16 insertions, 10 deletions
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 41fdb3e6ba..670b12fc82 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1058,6 +1058,10 @@ typedef struct SelectStmt
  * 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).
+ * The resolved common column collations are provided too; but note that if
+ * it's not UNION ALL, it's okay for a column to not have a common collation,
+ * so a member of the colCollations list could be InvalidOid even though the
+ * column has a collatable type.
  * ----------------------
  */
 typedef struct SetOperationStmt
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index efc79186f9..764fc36521 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -508,11 +508,11 @@ typedef struct NestLoopParam
  *		merge join node
  *
  * The expected ordering of each mergeable column is described by a btree
- * opfamily OID, a direction (BTLessStrategyNumber or BTGreaterStrategyNumber)
- * and a nulls-first flag.	Note that the two sides of each mergeclause may
- * be of different datatypes, but they are ordered the same way according to
- * the common opfamily.  The operator in each mergeclause must be an equality
- * operator of the indicated opfamily.
+ * opfamily OID, a collation OID, a direction (BTLessStrategyNumber or
+ * BTGreaterStrategyNumber) and a nulls-first flag.  Note that the two sides
+ * of each mergeclause may be of different datatypes, but they are ordered the
+ * same way according to the common opfamily and collation.  The operator in
+ * each mergeclause must be an equality operator of the indicated opfamily.
  * ----------------
  */
 typedef struct MergeJoin
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 609f253c07..47e5719321 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1047,9 +1047,9 @@ typedef struct CoerceToDomain
  * constraint.	This is effectively like a Param, but can be implemented more
  * simply since we need only one replacement value at a time.
  *
- * Note: the typeId/typeMod will be set from the domain's base type, not
- * the domain itself.  This is because we shouldn't consider the value to
- * be a member of the domain if we haven't yet checked its constraints.
+ * Note: the typeId/typeMod/collation will be set from the domain's base type,
+ * not the domain itself.  This is because we shouldn't consider the value
+ * to be a member of the domain if we haven't yet checked its constraints.
  */
 typedef struct CoerceToDomainValue
 {
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index f340f18b41..ab7ae2ebbd 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -423,7 +423,9 @@ typedef struct RelOptInfo
  * IndexOptInfo
  *		Per-index information for planning/optimization
  *
- *		opfamily[], indexkeys[], and opcintype[] each have ncolumns entries.
+ *		indexkeys[], indexcollations[], opfamily[], and opcintype[]
+ *		each have ncolumns entries.
+ *
  *		sortopfamily[], reverse_sort[], and nulls_first[] likewise have
  *		ncolumns entries, if the index is ordered; but if it is unordered,
  *		those pointers are NULL.
@@ -453,9 +455,9 @@ typedef struct IndexOptInfo
 
 	/* index descriptor information */
 	int			ncolumns;		/* number of columns in index */
-	Oid		   *opfamily;		/* OIDs of operator families for columns */
 	int		   *indexkeys;		/* column numbers of index's keys, or 0 */
 	Oid		   *indexcollations;	/* OIDs of collations of index columns */
+	Oid		   *opfamily;		/* OIDs of operator families for columns */
 	Oid		   *opcintype;		/* OIDs of opclass declared input data types */
 	Oid		   *sortopfamily;	/* OIDs of btree opfamilies, if orderable */
 	bool	   *reverse_sort;	/* is sort order descending? */