Improve handling of SET ACCESS METHOD for ALTER MATERIALIZED VIEW

b048326 has added support for SET ACCESS METHOD in ALTER TABLE, but it
has missed a few things for materialized views:
- No documentation for this clause on the ALTER MATERIALIZED VIEW page.
- psql tab completion missing.
- No regression tests.

This commit closes the gap on all the points listed above.

Author: Yugo Nagata
Discussion: https://postgr.es/m/20220316133337.5dc9740abfa24c25ec9f67f5@sraoss.co.jp

doc/src/sgml/ref/alter_materialized_view.sgml

@@ -43,6 +43,7 @@ ALTER MATERIALIZED VIEW ALL IN TABLESPACE <replaceable class="parameter">name</r
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET COMPRESSION <replaceable class="parameter">compression_method</replaceable>
     CLUSTER ON <replaceable class="parameter">index_name</replaceable>
     SET WITHOUT CLUSTER
+    SET ACCESS METHOD <replaceable class="parameter">new_access_method</replaceable>
     SET TABLESPACE <replaceable class="parameter">new_tablespace</replaceable>
     SET ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] )
     RESET ( <replaceable class="parameter">storage_parameter</replaceable> [, ... ] )

src/bin/psql/tab-complete.c

@@ -2124,7 +2124,11 @@ psql_completion(const char *text, int start, int end)
 		COMPLETE_WITH("TO");
 	/* ALTER MATERIALIZED VIEW xxx SET */
 	else if (Matches("ALTER", "MATERIALIZED", "VIEW", MatchAny, "SET"))
-		COMPLETE_WITH("(", "SCHEMA", "TABLESPACE", "WITHOUT CLUSTER");
+		COMPLETE_WITH("(", "ACCESS METHOD", "SCHEMA", "TABLESPACE", "WITHOUT CLUSTER");
+	/* ALTER MATERIALIZED VIEW xxx SET ACCESS METHOD */
+	else if (Matches("ALTER", "MATERIALIZED", "VIEW", MatchAny, "SET", "ACCESS", "METHOD"))
+		COMPLETE_WITH_QUERY(Query_for_list_of_table_access_methods);
+
 	/* ALTER POLICY <name> */
 	else if (Matches("ALTER", "POLICY"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_policies);

src/test/regress/expected/create_am.out

@@ -254,9 +254,35 @@ SELECT COUNT(a), COUNT(1) FILTER(WHERE a=1) FROM heaptable;
      9 |     1
 (1 row)
 
+-- ALTER MATERIALIZED VIEW SET ACCESS METHOD
+CREATE MATERIALIZED VIEW heapmv USING heap AS SELECT * FROM heaptable;
+SELECT amname FROM pg_class c, pg_am am
+  WHERE c.relam = am.oid AND c.oid = 'heapmv'::regclass;
+ amname 
+--------
+ heap
+(1 row)
+
+ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap2;
+SELECT amname FROM pg_class c, pg_am am
+  WHERE c.relam = am.oid AND c.oid = 'heapmv'::regclass;
+ amname 
+--------
+ heap2
+(1 row)
+
+SELECT COUNT(a), COUNT(1) FILTER(WHERE a=1) FROM heapmv;
+ count | count 
+-------+-------
+     9 |     1
+(1 row)
+
 -- No support for multiple subcommands
 ALTER TABLE heaptable SET ACCESS METHOD heap, SET ACCESS METHOD heap2;
 ERROR:  cannot have multiple SET ACCESS METHOD subcommands
+ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap, SET ACCESS METHOD heap2;
+ERROR:  cannot have multiple SET ACCESS METHOD subcommands
+DROP MATERIALIZED VIEW heapmv;
 DROP TABLE heaptable;
 -- No support for partitioned tables.
 CREATE TABLE am_partitioned(x INT, y INT)

src/test/regress/sql/create_am.sql

@@ -170,8 +170,18 @@ ALTER TABLE heaptable SET ACCESS METHOD heap2;
 SELECT amname FROM pg_class c, pg_am am
   WHERE c.relam = am.oid AND c.oid = 'heaptable'::regclass;
 SELECT COUNT(a), COUNT(1) FILTER(WHERE a=1) FROM heaptable;
+-- ALTER MATERIALIZED VIEW SET ACCESS METHOD
+CREATE MATERIALIZED VIEW heapmv USING heap AS SELECT * FROM heaptable;
+SELECT amname FROM pg_class c, pg_am am
+  WHERE c.relam = am.oid AND c.oid = 'heapmv'::regclass;
+ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap2;
+SELECT amname FROM pg_class c, pg_am am
+  WHERE c.relam = am.oid AND c.oid = 'heapmv'::regclass;
+SELECT COUNT(a), COUNT(1) FILTER(WHERE a=1) FROM heapmv;
 -- No support for multiple subcommands
 ALTER TABLE heaptable SET ACCESS METHOD heap, SET ACCESS METHOD heap2;
+ALTER MATERIALIZED VIEW heapmv SET ACCESS METHOD heap, SET ACCESS METHOD heap2;
+DROP MATERIALIZED VIEW heapmv;
 DROP TABLE heaptable;
 -- No support for partitioned tables.
 CREATE TABLE am_partitioned(x INT, y INT)