Add function of get_immv_def()

This function can reconstruct the underlying SELECT command for a
IMMV. (This is a decompiled reconstruction, not the original text
of the command)

expected/create_immv.out

@@ -16,11 +16,14 @@ NOTICE:  created index "mv2_index" on immv "mv2"
 
 SELECT create_immv('mv3', 'WITH d AS (DELETE FROM t RETURNING NULL) SELECT * FROM t');
 ERROR:  materialized views must not use data-modifying statements in WITH
-SELECT immvrelid FROM pg_ivm_immv ORDER BY 1;
- immvrelid 
------------
- mv
- mv2
+SELECT immvrelid, get_immv_def(immvrelid) FROM pg_ivm_immv ORDER BY 1;
+ immvrelid |     get_immv_def      
+-----------+-----------------------
+ mv        |  SELECT i            +
+           |    FROM t
+ mv2       |  SELECT i            +
+           |    FROM t            +
+           |   WHERE ((i % 2) = 0)
 (2 rows)
 
 DROP TABLE t;
@@ -29,16 +32,18 @@ DETAIL:  table mv depends on table t
 table mv2 depends on table t
 HINT:  Use DROP ... CASCADE to drop the dependent objects too.
 DROP TABLE mv;
-SELECT immvrelid FROM pg_ivm_immv ORDER BY 1;
- immvrelid 
------------
- mv2
+SELECT immvrelid, get_immv_def(immvrelid) FROM pg_ivm_immv ORDER BY 1;
+ immvrelid |     get_immv_def      
+-----------+-----------------------
+ mv2       |  SELECT i            +
+           |    FROM t            +
+           |   WHERE ((i % 2) = 0)
 (1 row)
 
 DROP TABLE mv2;
-SELECT immvrelid FROM pg_ivm_immv ORDER BY 1;
- immvrelid 
------------
+SELECT immvrelid, get_immv_def(immvrelid) FROM pg_ivm_immv ORDER BY 1;
+ immvrelid | get_immv_def 
+-----------+--------------
 (0 rows)
 
 DROP TABLE t;

pg_ivm--1.2--1.3.sql

@@ -5,3 +5,9 @@ RETURNS bool
 STABLE
 AS 'MODULE_PATHNAME', 'ivm_visible_in_prestate'
 LANGUAGE C;
+
+CREATE FUNCTION get_immv_def(IN immvrelid regclass)
+RETURNS text
+STRICT
+AS 'MODULE_PATHNAME', 'get_immv_def'
+LANGUAGE C;

pg_ivm.c

@@ -11,6 +11,7 @@
  */
 #include "postgres.h"
 
+#include "access/table.h"
 #include "access/xact.h"
 #include "catalog/dependency.h"
 #include "catalog/namespace.h"
@@ -45,6 +46,7 @@ static void parseNameAndColumns(const char *string, List **names, List **colName
 PG_FUNCTION_INFO_V1(create_immv);
 PG_FUNCTION_INFO_V1(refresh_immv);
 PG_FUNCTION_INFO_V1(IVM_prevent_immv_change);
+PG_FUNCTION_INFO_V1(get_immv_def);
 
 /*
  * Call back functions for cleaning up
@@ -320,3 +322,22 @@ PgIvmImmvPrimaryKeyIndexId(void)
 	return pg_ivm_immv_pkey_id;
 }
 
+/*
+ * Return the SELECT part of a IMMV
+ */
+Datum
+get_immv_def(PG_FUNCTION_ARGS)
+{
+	Oid	matviewOid = PG_GETARG_OID(0);
+	Relation matviewRel = NULL;
+	char * querystring = NULL;
+
+	matviewRel = table_open(matviewOid, AccessShareLock);
+	/* Make sure IMMV is a table. */
+	Assert(matviewRel->rd_rel->relkind == RELKIND_RELATION);
+
+	querystring = pg_ivm_get_querydef(get_immv_query(matviewRel), false);
+
+	table_close(matviewRel, NoLock);
+	PG_RETURN_TEXT_P(cstring_to_text(querystring));
+}

pg_ivm.h

@@ -43,6 +43,7 @@ extern void makeIvmAggColumn(ParseState *pstate, Aggref *aggref, char *resname,
 
 /* matview.c */
 
+extern Query *get_immv_query(Relation matviewRel);
 extern ObjectAddress ExecRefreshImmv(const RangeVar *relation, bool skipData,
 									 const char *queryString, QueryCompletion *qc);
 extern bool ImmvIncrementalMaintenanceIsEnabled(void);

sql/create_immv.sql

@@ -6,14 +6,14 @@ SELECT create_immv(' mv2 ( x  ) ', 'SELECT * FROM t WHERE i%2 = 0');
 
 SELECT create_immv('mv3', 'WITH d AS (DELETE FROM t RETURNING NULL) SELECT * FROM t');
 
-SELECT immvrelid FROM pg_ivm_immv ORDER BY 1;
+SELECT immvrelid, get_immv_def(immvrelid) FROM pg_ivm_immv ORDER BY 1;
 
 DROP TABLE t;
 
 DROP TABLE mv;
-SELECT immvrelid FROM pg_ivm_immv ORDER BY 1;
+SELECT immvrelid, get_immv_def(immvrelid) FROM pg_ivm_immv ORDER BY 1;
 
 DROP TABLE mv2;
-SELECT immvrelid FROM pg_ivm_immv ORDER BY 1;
+SELECT immvrelid, get_immv_def(immvrelid) FROM pg_ivm_immv ORDER BY 1;
 
 DROP TABLE t;