Properly handle IF NOT EXISTS for ADD COLUMN

src/backend/distributed/commands/table.c

@@ -120,7 +120,8 @@ static void SetInterShardDDLTaskRelationShardList(Task *task,
 static Oid get_attrdef_oid(Oid relationId, AttrNumber attnum);
 
 static char * GetAddColumnWithNextvalDefaultCmd(Oid sequenceOid, Oid relationId,
-												char *colname, TypeName *typeName);
+												char *colname, TypeName *typeName,
+												bool ifNotExists);
 static void ErrorIfAlterTableDropTableNameFromPostgresFdw(List *optionList, Oid
 														  relationId);
 
@@ -2650,7 +2651,9 @@ PostprocessAlterTableStmt(AlterTableStmt *alterTableStatement)
 																		  columnDefinition
 																		  ->colname,
 																		  columnDefinition
-																		  ->typeName);
+																		  ->typeName,
+																		  command->
+																		  missing_ok);
 								}
 							}
 						}
@@ -2915,7 +2918,7 @@ GetAlterColumnWithNextvalDefaultCmd(Oid sequenceOid, Oid relationId, char *colna
  */
 static char *
 GetAddColumnWithNextvalDefaultCmd(Oid sequenceOid, Oid relationId, char *colname,
-								  TypeName *typeName)
+								  TypeName *typeName, bool ifNotExists)
 {
 	char *qualifiedSequenceName = generate_qualified_relation_name(sequenceOid);
 	char *qualifiedRelationName = generate_qualified_relation_name(relationId);
@@ -2940,8 +2943,9 @@ GetAddColumnWithNextvalDefaultCmd(Oid sequenceOid, Oid relationId, char *colname
 	StringInfoData str = { 0 };
 	initStringInfo(&str);
 	appendStringInfo(&str,
-					 "ALTER TABLE %s ADD COLUMN %s %s "
+					 "ALTER TABLE %s ADD COLUMN %s %s %s "
-					 "DEFAULT %s(%s::regclass)", qualifiedRelationName, colname,
+					 "DEFAULT %s(%s::regclass)", qualifiedRelationName,
+					 ifNotExists ? "IF NOT EXISTS" : "", colname,
 					 format_type_extended(typeOid, typmod, formatFlags),
 					 quote_qualified_identifier("pg_catalog", nextvalFunctionName),
 					 quote_literal_cstr(qualifiedSequenceName));

src/backend/distributed/deparser/deparse_table_stmts.c

@@ -475,6 +475,11 @@ AppendAlterTableCmdAddColumn(StringInfo buf, AlterTableCmd *alterTableCmd)
 
 	appendStringInfoString(buf, " ADD COLUMN ");
 
+	if (alterTableCmd->missing_ok)
+	{
+		appendStringInfoString(buf, "IF NOT EXISTS ");
+	}
+
 	ColumnDef *columnDefinition = (ColumnDef *) alterTableCmd->def;
 
 	/*

src/test/regress/expected/multi_sequence_default.out

@@ -143,6 +143,8 @@ SELECT create_distributed_table('seq_test_4','x');
 
 CREATE SEQUENCE seq_4;
 ALTER TABLE seq_test_4 ADD COLUMN a bigint DEFAULT nextval('seq_4');
+ALTER TABLE seq_test_4 ADD COLUMN IF NOT EXISTS a bigint DEFAULT nextval('seq_4');
+NOTICE:  column "a" of relation "seq_test_4" already exists, skipping
 DROP SEQUENCE seq_4 CASCADE;
 NOTICE:  drop cascades to default value for column a of table seq_test_4
 TRUNCATE seq_test_4;
@@ -879,7 +881,7 @@ ROLLBACK;
 -- Show that existing sequence has been renamed and a new sequence with the same name
 -- created for another type
 \c - - - :worker_1_port
-SELECT seqrelid::regclass, seqtypid::regtype, seqmax, seqmin FROM pg_sequence WHERE seqrelid::regclass::text like '%sequence_rollback%' ORDER BY 1,2;
+SELECT seqrelid::regclass, seqtypid::regtype, seqmax, seqmin FROM pg_sequence WHERE seqrelid::regclass::text in ('sequence_rollback', '"sequence_rollback(citus_backup_0)"') ORDER BY 1,2;
               seqrelid               | seqtypid |     seqmax      |     seqmin
 ---------------------------------------------------------------------
  "sequence_rollback(citus_backup_0)" | integer  |      2147483647 |               1

src/test/regress/sql/multi_sequence_default.sql

@@ -65,6 +65,7 @@ CREATE TABLE seq_test_4 (x int, y int);
 SELECT create_distributed_table('seq_test_4','x');
 CREATE SEQUENCE seq_4;
 ALTER TABLE seq_test_4 ADD COLUMN a bigint DEFAULT nextval('seq_4');
+ALTER TABLE seq_test_4 ADD COLUMN IF NOT EXISTS a bigint DEFAULT nextval('seq_4');
 DROP SEQUENCE seq_4 CASCADE;
 TRUNCATE seq_test_4;
 CREATE SEQUENCE seq_4;
@@ -440,7 +441,7 @@ ROLLBACK;
 -- Show that existing sequence has been renamed and a new sequence with the same name
 -- created for another type
 \c - - - :worker_1_port
-SELECT seqrelid::regclass, seqtypid::regtype, seqmax, seqmin FROM pg_sequence WHERE seqrelid::regclass::text like '%sequence_rollback%' ORDER BY 1,2;
+SELECT seqrelid::regclass, seqtypid::regtype, seqmax, seqmin FROM pg_sequence WHERE seqrelid::regclass::text in ('sequence_rollback', '"sequence_rollback(citus_backup_0)"') ORDER BY 1,2;
 
 \c - - - :master_port