Sanitize IF NOT EXISTS in EXPLAIN for CTAS and matviews

IF NOT EXISTS was ignored when specified in an EXPLAIN query for CREATE
MATERIALIZED VIEW or CREATE TABLE AS.  Hence, if this clause was
specified, the caller would get a failure if the relation already
exists instead of a success with a NOTICE message.

This commit makes the behavior of IF NOT EXISTS in EXPLAIN consistent
with the non-EXPLAIN'd DDL queries, preventing a failure with IF NOT
EXISTS if the relation to-be-created already exists.  The skip is done
before the SELECT query used for the relation is planned or executed,
and a "dummy" plan is generated instead depending on the format used by
EXPLAIN.

Author: Bharath Rupireddy
Reviewed-by: Zhijie Hou, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACVa3oJ9O_wcGd+FtHWZds04dEKcakxphGz5POVgD4wC7Q@mail.gmail.com

7 files changed, 180 insertions, 15 deletions

diff --git a/src/backend/commands/createas.c b/src/backend/commands/createas.c
index 6bf6c5a3106..009896bcee7 100644
--- a/src/backend/commands/createas.c
+++ b/src/backend/commands/createas.c
@@ -239,21 +239,9 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 	PlannedStmt *plan;
 	QueryDesc  *queryDesc;
 
-	if (stmt->if_not_exists)
-	{
-		Oid			nspid;
-
-		nspid = RangeVarGetCreationNamespace(stmt->into->rel);
-
-		if (get_relname_relid(stmt->into->rel->relname, nspid))
-		{
-			ereport(NOTICE,
-					(errcode(ERRCODE_DUPLICATE_TABLE),
-					 errmsg("relation \"%s\" already exists, skipping",
-							stmt->into->rel->relname)));
-			return InvalidObjectAddress;
-		}
-	}
+	/* Check if the relation exists or not */
+	if (CreateTableAsRelExists(stmt))
+		return InvalidObjectAddress;
 
 	/*
 	 * Create the tuple receiver object and insert info it will need
@@ -401,6 +389,41 @@ GetIntoRelEFlags(IntoClause *intoClause)
 }
 
 /*
+ * CreateTableAsRelExists --- check existence of relation for CreateTableAsStmt
+ *
+ * Utility wrapper checking if the relation pending for creation in this
+ * CreateTableAsStmt query already exists or not.  Returns true if the
+ * relation exists, otherwise false.
+ */
+bool
+CreateTableAsRelExists(CreateTableAsStmt *ctas)
+{
+	Oid			nspid;
+	IntoClause *into = ctas->into;
+
+	nspid = RangeVarGetCreationNamespace(into->rel);
+
+	if (get_relname_relid(into->rel->relname, nspid))
+	{
+		if (!ctas->if_not_exists)
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_TABLE),
+					 errmsg("relation \"%s\" already exists",
+							into->rel->relname)));
+
+		/* The relation exists and IF NOT EXISTS has been specified */
+		ereport(NOTICE,
+				(errcode(ERRCODE_DUPLICATE_TABLE),
+				 errmsg("relation \"%s\" already exists, skipping",
+						into->rel->relname)));
+		return true;
+	}
+
+	/* Relation does not exist, it can be created */
+	return false;
+}
+
+/*
  * CreateIntoRelDestReceiver -- create a suitable DestReceiver object
  *
  * intoClause will be NULL if called from CreateDestReceiver(), in which
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 43f9b01e833..d797b5f53e0 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -435,6 +435,22 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 		CreateTableAsStmt *ctas = (CreateTableAsStmt *) utilityStmt;
 		List	   *rewritten;
 
+		/*
+		 * Check if the relation exists or not.  This is done at this stage to
+		 * avoid query planning or execution.
+		 */
+		if (CreateTableAsRelExists(ctas))
+		{
+			if (ctas->objtype == OBJECT_TABLE)
+				ExplainDummyGroup("CREATE TABLE AS", NULL, es);
+			else if (ctas->objtype == OBJECT_MATVIEW)
+				ExplainDummyGroup("CREATE MATERIALIZED VIEW", NULL, es);
+			else
+				elog(ERROR,	"unexpected object type: %d",
+					 (int) ctas->objtype);
+			return;
+		}
+
 		rewritten = QueryRewrite(castNode(Query, copyObject(ctas->query)));
 		Assert(list_length(rewritten) == 1);
 		ExplainOneQuery(linitial_node(Query, rewritten),
diff --git a/src/include/commands/createas.h b/src/include/commands/createas.h
index 76292302542..d8cfb625228 100644
--- a/src/include/commands/createas.h
+++ b/src/include/commands/createas.h
@@ -29,4 +29,6 @@ extern int	GetIntoRelEFlags(IntoClause *intoClause);
 
 extern DestReceiver *CreateIntoRelDestReceiver(IntoClause *intoClause);
 
+extern bool CreateTableAsRelExists(CreateTableAsStmt *ctas);
+
 #endif							/* CREATEAS_H */
diff --git a/src/test/regress/expected/matview.out b/src/test/regress/expected/matview.out
index 2c0760404d3..4b3a2e0cb73 100644
--- a/src/test/regress/expected/matview.out
+++ b/src/test/regress/expected/matview.out
@@ -630,3 +630,41 @@ drop cascades to materialized view matview_schema.mv_withdata2
 drop cascades to materialized view matview_schema.mv_nodata1
 drop cascades to materialized view matview_schema.mv_nodata2
 DROP USER regress_matview_user;
+-- CREATE MATERIALIZED VIEW ... IF NOT EXISTS
+CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1;
+CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
+ERROR:  relation "matview_ine_tab" already exists
+CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+  SELECT 1 / 0; -- ok
+NOTICE:  relation "matview_ine_tab" already exists, skipping
+CREATE MATERIALIZED VIEW matview_ine_tab AS
+  SELECT 1 / 0 WITH NO DATA; -- error
+ERROR:  relation "matview_ine_tab" already exists
+CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+  SELECT 1 / 0 WITH NO DATA; -- ok
+NOTICE:  relation "matview_ine_tab" already exists, skipping
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW matview_ine_tab AS
+    SELECT 1 / 0; -- error
+ERROR:  relation "matview_ine_tab" already exists
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+    SELECT 1 / 0; -- ok
+NOTICE:  relation "matview_ine_tab" already exists, skipping
+ QUERY PLAN 
+------------
+(0 rows)
+
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW matview_ine_tab AS
+    SELECT 1 / 0 WITH NO DATA; -- error
+ERROR:  relation "matview_ine_tab" already exists
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+    SELECT 1 / 0 WITH NO DATA; -- ok
+NOTICE:  relation "matview_ine_tab" already exists, skipping
+ QUERY PLAN 
+------------
+(0 rows)
+
+DROP MATERIALIZED VIEW matview_ine_tab;
diff --git a/src/test/regress/expected/select_into.out b/src/test/regress/expected/select_into.out
index bf5c6bea045..43b8209d229 100644
--- a/src/test/regress/expected/select_into.out
+++ b/src/test/regress/expected/select_into.out
@@ -178,3 +178,45 @@ INSERT INTO b SELECT 1 INTO f;
 ERROR:  SELECT ... INTO is not allowed here
 LINE 1: INSERT INTO b SELECT 1 INTO f;
                                     ^
+-- Test CREATE TABLE AS ... IF NOT EXISTS
+CREATE TABLE ctas_ine_tbl AS SELECT 1;
+CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0; -- error
+ERROR:  relation "ctas_ine_tbl" already exists
+CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0; -- ok
+NOTICE:  relation "ctas_ine_tbl" already exists, skipping
+CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- error
+ERROR:  relation "ctas_ine_tbl" already exists
+CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- ok
+NOTICE:  relation "ctas_ine_tbl" already exists, skipping
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0; -- error
+ERROR:  relation "ctas_ine_tbl" already exists
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0; -- ok
+NOTICE:  relation "ctas_ine_tbl" already exists, skipping
+ QUERY PLAN 
+------------
+(0 rows)
+
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- error
+ERROR:  relation "ctas_ine_tbl" already exists
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- ok
+NOTICE:  relation "ctas_ine_tbl" already exists, skipping
+ QUERY PLAN 
+------------
+(0 rows)
+
+PREPARE ctas_ine_query AS SELECT 1 / 0;
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE ctas_ine_tbl AS EXECUTE ctas_ine_query; -- error
+ERROR:  relation "ctas_ine_tbl" already exists
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS EXECUTE ctas_ine_query; -- ok
+NOTICE:  relation "ctas_ine_tbl" already exists, skipping
+ QUERY PLAN 
+------------
+(0 rows)
+
+DROP TABLE ctas_ine_tbl;
diff --git a/src/test/regress/sql/matview.sql b/src/test/regress/sql/matview.sql
index 70c4954d89a..4a4bd0d6b61 100644
--- a/src/test/regress/sql/matview.sql
+++ b/src/test/regress/sql/matview.sql
@@ -264,3 +264,26 @@ ALTER DEFAULT PRIVILEGES FOR ROLE regress_matview_user
 
 DROP SCHEMA matview_schema CASCADE;
 DROP USER regress_matview_user;
+
+-- CREATE MATERIALIZED VIEW ... IF NOT EXISTS
+CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1;
+CREATE MATERIALIZED VIEW matview_ine_tab AS SELECT 1 / 0; -- error
+CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+  SELECT 1 / 0; -- ok
+CREATE MATERIALIZED VIEW matview_ine_tab AS
+  SELECT 1 / 0 WITH NO DATA; -- error
+CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+  SELECT 1 / 0 WITH NO DATA; -- ok
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW matview_ine_tab AS
+    SELECT 1 / 0; -- error
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+    SELECT 1 / 0; -- ok
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW matview_ine_tab AS
+    SELECT 1 / 0 WITH NO DATA; -- error
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE MATERIALIZED VIEW IF NOT EXISTS matview_ine_tab AS
+    SELECT 1 / 0 WITH NO DATA; -- ok
+DROP MATERIALIZED VIEW matview_ine_tab;
diff --git a/src/test/regress/sql/select_into.sql b/src/test/regress/sql/select_into.sql
index 6c170ef9688..7e903c339a8 100644
--- a/src/test/regress/sql/select_into.sql
+++ b/src/test/regress/sql/select_into.sql
@@ -115,3 +115,24 @@ COPY (SELECT 1 INTO frak UNION SELECT 2) TO 'blob';
 SELECT * FROM (SELECT 1 INTO f) bar;
 CREATE VIEW foo AS SELECT 1 INTO b;
 INSERT INTO b SELECT 1 INTO f;
+
+-- Test CREATE TABLE AS ... IF NOT EXISTS
+CREATE TABLE ctas_ine_tbl AS SELECT 1;
+CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0; -- error
+CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0; -- ok
+CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- error
+CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- ok
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0; -- error
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0; -- ok
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- error
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS SELECT 1 / 0 WITH NO DATA; -- ok
+PREPARE ctas_ine_query AS SELECT 1 / 0;
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE ctas_ine_tbl AS EXECUTE ctas_ine_query; -- error
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+  CREATE TABLE IF NOT EXISTS ctas_ine_tbl AS EXECUTE ctas_ine_query; -- ok
+DROP TABLE ctas_ine_tbl;