Restructure SELECT INTO's parsetree representation into CreateTableAsStmt.

Making this operation look like a utility statement seems generally a good
idea, and particularly so in light of the desire to provide command
triggers for utility statements.  The original choice of representing it as
SELECT with an IntoClause appendage had metastasized into rather a lot of
places, unfortunately, so that this patch is a great deal more complicated
than one might at first expect.

In particular, keeping EXPLAIN working for SELECT INTO and CREATE TABLE AS
subcommands required restructuring some EXPLAIN-related APIs.  Add-on code
that calls ExplainOnePlan or ExplainOneUtility, or uses
ExplainOneQuery_hook, will need adjustment.

Also, the cases PREPARE ... SELECT INTO and CREATE RULE ... SELECT INTO,
which formerly were accepted though undocumented, are no longer accepted.
The PREPARE case can be replaced with use of CREATE TABLE AS EXECUTE.
The CREATE RULE case doesn't seem to have much real-world use (since the
rule would work only once before failing with "table already exists"),
so we'll not bother with that one.

Both SELECT INTO and CREATE TABLE AS still return a command tag of
"SELECT nnnn".  There was some discussion of returning "CREATE TABLE nnnn",
but for the moment backwards compatibility wins the day.

Andres Freund and Tom Lane

5 files changed, 13 insertions, 20 deletions

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 8bbe97713bb..6b0541b9b59 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -233,7 +233,6 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->rtable = glob->finalrtable;
 	result->resultRelations = glob->resultRelations;
 	result->utilityStmt = parse->utilityStmt;
-	result->intoClause = parse->intoClause;
 	result->subplans = glob->subplans;
 	result->rewindPlanIDs = glob->rewindPlanIDs;
 	result->rowMarks = glob->finalrowmarks;
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 69396694aaa..9e347ce7360 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -22,6 +22,7 @@
 #include "optimizer/pathnode.h"
 #include "optimizer/planmain.h"
 #include "optimizer/tlist.h"
+#include "tcop/utility.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
@@ -1887,16 +1888,14 @@ extract_query_dependencies_walker(Node *node, PlannerInfo *context)
 		Query	   *query = (Query *) node;
 		ListCell   *lc;
 
-		if (query->commandType == CMD_UTILITY)
+		while (query->commandType == CMD_UTILITY)
 		{
-			/* Ignore utility statements, except EXPLAIN */
-			if (IsA(query->utilityStmt, ExplainStmt))
-			{
-				query = (Query *) ((ExplainStmt *) query->utilityStmt)->query;
-				Assert(IsA(query, Query));
-				Assert(query->commandType != CMD_UTILITY);
-			}
-			else
+			/*
+			 * Ignore utility statements, except those (such as EXPLAIN) that
+			 * contain a parsed-but-not-planned query.
+			 */
+			query = UtilityContainsQuery(query->utilityStmt);
+			if (query == NULL)
 				return false;
 		}
 
diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index b64db1e1c06..f30f02f266d 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -1399,7 +1399,6 @@ simplify_EXISTS_query(Query *query)
 	 * are complex.
 	 */
 	if (query->commandType != CMD_SELECT ||
-		query->intoClause ||
 		query->setOperations ||
 		query->hasAggs ||
 		query->hasWindowFuncs ||
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 2fd795b4592..c1b2f1db11a 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -1136,8 +1136,7 @@ is_simple_subquery(Query *subquery)
 	 */
 	if (!IsA(subquery, Query) ||
 		subquery->commandType != CMD_SELECT ||
-		subquery->utilityStmt != NULL ||
-		subquery->intoClause != NULL)
+		subquery->utilityStmt != NULL)
 		elog(ERROR, "subquery is bogus");
 
 	/*
@@ -1223,8 +1222,7 @@ is_simple_union_all(Query *subquery)
 	/* Let's just make sure it's a valid subselect ... */
 	if (!IsA(subquery, Query) ||
 		subquery->commandType != CMD_SELECT ||
-		subquery->utilityStmt != NULL ||
-		subquery->intoClause != NULL)
+		subquery->utilityStmt != NULL)
 		elog(ERROR, "subquery is bogus");
 
 	/* Is it a set-operation query at all? */
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index cd3da46bc5e..b14ae2e3670 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -4158,7 +4158,7 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	pstate->p_sourcetext = src;
 	sql_fn_parser_setup(pstate, pinfo);
 
-	querytree = transformStmt(pstate, linitial(raw_parsetree_list));
+	querytree = transformTopLevelStmt(pstate, linitial(raw_parsetree_list));
 
 	free_parsestate(pstate);
 
@@ -4168,7 +4168,6 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	if (!IsA(querytree, Query) ||
 		querytree->commandType != CMD_SELECT ||
 		querytree->utilityStmt ||
-		querytree->intoClause ||
 		querytree->hasAggs ||
 		querytree->hasWindowFuncs ||
 		querytree->hasSubLinks ||
@@ -4678,12 +4677,11 @@ inline_set_returning_function(PlannerInfo *root, RangeTblEntry *rte)
 	querytree = linitial(querytree_list);
 
 	/*
-	 * The single command must be a regular results-returning SELECT.
+	 * The single command must be a plain SELECT.
 	 */
 	if (!IsA(querytree, Query) ||
 		querytree->commandType != CMD_SELECT ||
-		querytree->utilityStmt ||
-		querytree->intoClause)
+		querytree->utilityStmt)
 		goto fail;
 
 	/*