Fix the incorrect column count after ALTER TABLE, this fixes the bug #7378 (please read the analysis in the bug for more information)

src/backend/distributed/deparser/ruleutils_15.c

@@ -1563,8 +1563,15 @@ set_join_column_names(deparse_namespace *dpns, RangeTblEntry *rte,
 
 	/* Assert we processed the right number of columns */
 #ifdef USE_ASSERT_CHECKING
-	while (i < colinfo->num_cols && colinfo->colnames[i] == NULL)
+	for (int col_index = 0; col_index < colinfo->num_cols; col_index++)
-		i++;
+	{
+		/*
+		 * In the above processing-loops, "i" advances only if
+		 * the column is not new, check if this is a new column.
+		 */
+		if (colinfo->is_new_col[col_index])
+			i++;
+	}
 	Assert(i == colinfo->num_cols);
 	Assert(j == nnewcolumns);
 #endif

src/backend/distributed/utils/citus_nodefuncs.c

@@ -142,7 +142,17 @@ SetRangeTblExtraData(RangeTblEntry *rte, CitusRTEKind rteKind, char *fragmentSch
 	fauxFunction->funcexpr = (Node *) fauxFuncExpr;
 
 	/* set the column count to pass ruleutils checks, not used elsewhere */
-	fauxFunction->funccolcount = list_length(rte->eref->colnames);
+	if (rte->relid != 0)
+	{
+		Relation rel = RelationIdGetRelation(rte->relid);
+		fauxFunction->funccolcount = RelationGetNumberOfAttributes(rel);
+		RelationClose(rel);
+	}
+	else
+	{
+		fauxFunction->funccolcount = list_length(rte->eref->colnames);
+	}
+
 	fauxFunction->funccolnames = funcColumnNames;
 	fauxFunction->funccoltypes = funcColumnTypes;
 	fauxFunction->funccoltypmods = funcColumnTypeMods;

src/test/regress/expected/multi_alter_table_statements.out

@@ -1349,6 +1349,77 @@ SELECT pg_identify_object_as_address(classid, objid, objsubid) from pg_catalog.p
  (schema,{test_schema_for_sequence_propagation},{})
 (1 row)
 
+-- Bug: https://github.com/citusdata/citus/issues/7378
+-- Create a reference table
+CREATE TABLE tbl_ref(row_id integer primary key);
+INSERT INTO tbl_ref VALUES (1), (2);
+SELECT create_reference_table('tbl_ref');
+NOTICE:  Copying data from local table...
+NOTICE:  copying the data has completed
+DETAIL:  The local data in the table is no longer visible, but is still on disk.
+HINT:  To remove the local data, run: SELECT truncate_local_data_after_distributing_table($$multi_alter_table_statements.tbl_ref$$)
+ create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- Create a distributed table
+CREATE TABLE tbl_dist(series_id integer);
+INSERT INTO tbl_dist VALUES (1), (1), (2), (2);
+SELECT create_distributed_table('tbl_dist', 'series_id');
+NOTICE:  Copying data from local table...
+NOTICE:  copying the data has completed
+DETAIL:  The local data in the table is no longer visible, but is still on disk.
+HINT:  To remove the local data, run: SELECT truncate_local_data_after_distributing_table($$multi_alter_table_statements.tbl_dist$$)
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- Create a view that joins the distributed table with the reference table on the distribution key.
+CREATE VIEW vw_citus_views as
+SELECT d.series_id FROM tbl_dist d JOIN tbl_ref r ON d.series_id = r.row_id;
+-- The view initially works fine
+SELECT * FROM vw_citus_views ORDER BY 1;
+ series_id
+---------------------------------------------------------------------
+         1
+         1
+         2
+         2
+(4 rows)
+
+-- Now, alter the table
+ALTER TABLE tbl_ref ADD COLUMN category1 varchar(50);
+SELECT * FROM vw_citus_views ORDER BY 1;
+ series_id
+---------------------------------------------------------------------
+         1
+         1
+         2
+         2
+(4 rows)
+
+ALTER TABLE tbl_ref ADD COLUMN category2 varchar(50);
+SELECT * FROM vw_citus_views ORDER BY 1;
+ series_id
+---------------------------------------------------------------------
+         1
+         1
+         2
+         2
+(4 rows)
+
+ALTER TABLE tbl_ref DROP COLUMN category1;
+SELECT * FROM vw_citus_views ORDER BY 1;
+ series_id
+---------------------------------------------------------------------
+         1
+         1
+         2
+         2
+(4 rows)
+
 SET client_min_messages TO WARNING;
 DROP SCHEMA test_schema_for_sequence_propagation CASCADE;
 DROP TABLE table_without_sequence;

src/test/regress/sql/multi_alter_table_statements.sql

@@ -727,6 +727,32 @@ ALTER TABLE table_without_sequence ADD COLUMN x BIGINT DEFAULT nextval('test_sch
 SELECT pg_identify_object_as_address(classid, objid, objsubid) from pg_catalog.pg_dist_object WHERE objid IN ('test_schema_for_sequence_propagation.seq_10'::regclass);
 SELECT pg_identify_object_as_address(classid, objid, objsubid) from pg_catalog.pg_dist_object WHERE objid IN ('test_schema_for_sequence_propagation'::regnamespace);
 
+-- Bug: https://github.com/citusdata/citus/issues/7378
+
+-- Create a reference table
+CREATE TABLE tbl_ref(row_id integer primary key);
+INSERT INTO tbl_ref VALUES (1), (2);
+SELECT create_reference_table('tbl_ref');
+
+-- Create a distributed table
+CREATE TABLE tbl_dist(series_id integer);
+INSERT INTO tbl_dist VALUES (1), (1), (2), (2);
+SELECT create_distributed_table('tbl_dist', 'series_id');
+
+-- Create a view that joins the distributed table with the reference table on the distribution key.
+CREATE VIEW vw_citus_views as
+SELECT d.series_id FROM tbl_dist d JOIN tbl_ref r ON d.series_id = r.row_id;
+
+-- The view initially works fine
+SELECT * FROM vw_citus_views ORDER BY 1;
+-- Now, alter the table
+ALTER TABLE tbl_ref ADD COLUMN category1 varchar(50);
+SELECT * FROM vw_citus_views ORDER BY 1;
+ALTER TABLE tbl_ref ADD COLUMN category2 varchar(50);
+SELECT * FROM vw_citus_views ORDER BY 1;
+ALTER TABLE tbl_ref DROP COLUMN category1;
+SELECT * FROM vw_citus_views ORDER BY 1;
+
 SET client_min_messages TO WARNING;
 DROP SCHEMA test_schema_for_sequence_propagation CASCADE;
 DROP TABLE table_without_sequence;