Convert RelabelTypes into CollateExprs in get_rule_expr function

src/backend/distributed/deparser/ruleutils_11.c

@@ -5166,20 +5166,42 @@ get_rule_expr(Node *node, deparse_context *context,
 		case T_RelabelType:
 			{
 				RelabelType *relabel = (RelabelType *) node;
-				Node	   *arg = (Node *) relabel->arg;
 
-				if (relabel->relabelformat == COERCE_IMPLICIT_CAST &&
+				/*
-					!showimplicit)
+				 * This is a Citus specific modification
+				 * The planner converts CollateExpr to RelabelType
+				 * and here we convert back.
+				 */
+				if (relabel->resultcollid != InvalidOid)
 				{
-					/* don't show the implicit cast */
+					CollateExpr *collate = RelabelTypeToCollateExpr(relabel);
-					get_rule_expr_paren(arg, context, false, node);
+					Node	   *arg = (Node *) collate->arg;
+
+					if (!PRETTY_PAREN(context))
+						appendStringInfoChar(buf, '(');
+					get_rule_expr_paren(arg, context, showimplicit, node);
+					appendStringInfo(buf, " COLLATE %s",
+									generate_collation_name(collate->collOid));
+					if (!PRETTY_PAREN(context))
+						appendStringInfoChar(buf, ')');
 				}
 				else
 				{
-					get_coercion_expr(arg, context,
+					Node	   *arg = (Node *) relabel->arg;
-									  relabel->resulttype,
+
-									  relabel->resulttypmod,
+					if (relabel->relabelformat == COERCE_IMPLICIT_CAST &&
-									  node);
+						!showimplicit)
+					{
+						/* don't show the implicit cast */
+						get_rule_expr_paren(arg, context, false, node);
+					}
+					else
+					{
+						get_coercion_expr(arg, context,
+										  relabel->resulttype,
+										  relabel->resulttypmod,
+										  node);
+					}
 				}
 			}
 			break;

src/backend/distributed/deparser/ruleutils_12.c

@@ -5181,20 +5181,42 @@ get_rule_expr(Node *node, deparse_context *context,
 		case T_RelabelType:
 			{
 				RelabelType *relabel = (RelabelType *) node;
-				Node	   *arg = (Node *) relabel->arg;
 
-				if (relabel->relabelformat == COERCE_IMPLICIT_CAST &&
+				/*
-					!showimplicit)
+				 * This is a Citus specific modification
+				 * The planner converts CollateExpr to RelabelType
+				 * and here we convert back.
+				 */
+				if (relabel->resultcollid != InvalidOid)
 				{
-					/* don't show the implicit cast */
+					CollateExpr *collate = RelabelTypeToCollateExpr(relabel);
-					get_rule_expr_paren(arg, context, false, node);
+					Node	   *arg = (Node *) collate->arg;
+
+					if (!PRETTY_PAREN(context))
+						appendStringInfoChar(buf, '(');
+					get_rule_expr_paren(arg, context, showimplicit, node);
+					appendStringInfo(buf, " COLLATE %s",
+									generate_collation_name(collate->collOid));
+					if (!PRETTY_PAREN(context))
+						appendStringInfoChar(buf, ')');
 				}
 				else
 				{
-					get_coercion_expr(arg, context,
+					Node	   *arg = (Node *) relabel->arg;
-									  relabel->resulttype,
+
-									  relabel->resulttypmod,
+					if (relabel->relabelformat == COERCE_IMPLICIT_CAST &&
-									  node);
+						!showimplicit)
+					{
+						/* don't show the implicit cast */
+						get_rule_expr_paren(arg, context, false, node);
+					}
+					else
+					{
+						get_coercion_expr(arg, context,
+										  relabel->resulttype,
+										  relabel->resulttypmod,
+										  node);
+					}
 				}
 			}
 			break;

src/backend/distributed/deparser/ruleutils_13.c

@@ -5237,20 +5237,42 @@ get_rule_expr(Node *node, deparse_context *context,
 		case T_RelabelType:
 			{
 				RelabelType *relabel = (RelabelType *) node;
-				Node	   *arg = (Node *) relabel->arg;
 
-				if (relabel->relabelformat == COERCE_IMPLICIT_CAST &&
+				/*
-					!showimplicit)
+				 * This is a Citus specific modification
+				 * The planner converts CollateExpr to RelabelType
+				 * and here we convert back.
+				 */
+				if (relabel->resultcollid != InvalidOid)
 				{
-					/* don't show the implicit cast */
+					CollateExpr *collate = RelabelTypeToCollateExpr(relabel);
-					get_rule_expr_paren(arg, context, false, node);
+					Node	   *arg = (Node *) collate->arg;
+
+					if (!PRETTY_PAREN(context))
+						appendStringInfoChar(buf, '(');
+					get_rule_expr_paren(arg, context, showimplicit, node);
+					appendStringInfo(buf, " COLLATE %s",
+									generate_collation_name(collate->collOid));
+					if (!PRETTY_PAREN(context))
+						appendStringInfoChar(buf, ')');
 				}
 				else
 				{
-					get_coercion_expr(arg, context,
+					Node	   *arg = (Node *) relabel->arg;
-									  relabel->resulttype,
+
-									  relabel->resulttypmod,
+					if (relabel->relabelformat == COERCE_IMPLICIT_CAST &&
-									  node);
+						!showimplicit)
+					{
+						/* don't show the implicit cast */
+						get_rule_expr_paren(arg, context, false, node);
+					}
+					else
+					{
+						get_coercion_expr(arg, context,
+										  relabel->resulttype,
+										  relabel->resulttypmod,
+										  node);
+					}
 				}
 			}
 			break;

src/backend/distributed/planner/multi_physical_planner.c

@@ -2937,6 +2937,24 @@ SqlTaskList(Job *job)
 }
 
 
+/*
+ * RelabelTypeToCollateExpr converts RelabelType's into CollationExpr's.
+ * With that, we will be able to pushdown COLLATE's.
+ */
+CollateExpr *
+RelabelTypeToCollateExpr(RelabelType *relabelType)
+{
+	Assert(OidIsValid(relabelType->resultcollid));
+
+	CollateExpr *collateExpr = makeNode(CollateExpr);
+	collateExpr->arg = relabelType->arg;
+	collateExpr->collOid = relabelType->resultcollid;
+	collateExpr->location = relabelType->location;
+
+	return collateExpr;
+}
+
+
 /*
  * DependsOnHashPartitionJob checks if the given job depends on a hash
  * partitioning job.

src/include/distributed/multi_physical_planner.h

@@ -540,6 +540,7 @@ extern Node *  WrapUngroupedVarsInAnyValueAggregate(Node *expression,
 													List *groupClauseList,
 													List *targetList,
 													bool checkExpressionEquality);
+extern CollateExpr * RelabelTypeToCollateExpr(RelabelType *relabelType);
 
 /*
  * Function declarations for building, updating constraints and simple operator

src/test/regress/expected/distributed_collations.out

@@ -56,6 +56,44 @@ SELECT * FROM collation_tests.test_propagate WHERE t2 < 'b' COLLATE "C";
   2 | Voẞr | Vossr
 (1 row)
 
+SELECT * FROM collation_tests.test_propagate WHERE t2 COLLATE "C" < 'b';
+ id |  t1  |  t2
+---------------------------------------------------------------------
+  2 | Voẞr | Vossr
+(1 row)
+
+-- Test COLLATE is pushed down with aggregate function
+SET citus.next_shard_id TO 20060000;
+CREATE TABLE test_collate_pushed_down_aggregate (a int, b int);
+SELECT create_distributed_table('test_collate_pushed_down_aggregate', 'a');
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+SELECT alter_distributed_table('test_collate_pushed_down_aggregate', shard_count := 2, cascade_to_colocated:=false);
+NOTICE:  creating a new table for collation_tests.test_collate_pushed_down_aggregate
+NOTICE:  Moving the data of collation_tests.test_collate_pushed_down_aggregate
+NOTICE:  Dropping the old collation_tests.test_collate_pushed_down_aggregate
+NOTICE:  Renaming the new table to collation_tests.test_collate_pushed_down_aggregate
+ alter_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+SET citus.log_remote_commands TO true;
+SELECT ALL MIN((lower(CAST(test_collate_pushed_down_aggregate.a AS VARCHAR)) COLLATE "C"))
+    FROM ONLY test_collate_pushed_down_aggregate;
+NOTICE:  issuing SELECT min((lower(((a)::character varying COLLATE "default")) COLLATE "C")) AS min FROM collation_tests.test_collate_pushed_down_aggregate_20060004 test_collate_pushed_down_aggregate WHERE true
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+NOTICE:  issuing SELECT min((lower(((a)::character varying COLLATE "default")) COLLATE "C")) AS min FROM collation_tests.test_collate_pushed_down_aggregate_20060005 test_collate_pushed_down_aggregate WHERE true
+DETAIL:  on server postgres@localhost:xxxxx connectionId: xxxxxxx
+ min
+---------------------------------------------------------------------
+
+(1 row)
+
+RESET citus.log_remote_commands;
 -- Test range table with collated distribution column
 CREATE TABLE test_range(key text COLLATE german_phonebook, val int);
 SELECT create_distributed_table('test_range', 'key', 'range');

src/test/regress/sql/distributed_collations.sql

@@ -34,6 +34,17 @@ SELECT create_distributed_table('test_propagate', 'id');
 -- Test COLLATE is pushed down
 SELECT * FROM collation_tests.test_propagate WHERE t2 < 'b';
 SELECT * FROM collation_tests.test_propagate WHERE t2 < 'b' COLLATE "C";
+SELECT * FROM collation_tests.test_propagate WHERE t2 COLLATE "C" < 'b';
+
+-- Test COLLATE is pushed down with aggregate function
+SET citus.next_shard_id TO 20060000;
+CREATE TABLE test_collate_pushed_down_aggregate (a int, b int);
+SELECT create_distributed_table('test_collate_pushed_down_aggregate', 'a');
+SELECT alter_distributed_table('test_collate_pushed_down_aggregate', shard_count := 2, cascade_to_colocated:=false);
+SET citus.log_remote_commands TO true;
+SELECT ALL MIN((lower(CAST(test_collate_pushed_down_aggregate.a AS VARCHAR)) COLLATE "C"))
+    FROM ONLY test_collate_pushed_down_aggregate;
+RESET citus.log_remote_commands;
 
 -- Test range table with collated distribution column
 CREATE TABLE test_range(key text COLLATE german_phonebook, val int);