Fix readable CTE with SELECT INTO clause.

In #1215 bugfix, it add a check
for writable CTE with SELECT INTO clause. It will invoke
`transformWithClause` twice, even it's readable CTE. But Cloudberry
currently only support one WITH clause per query level, so it will lead
to crash.

So we can give up invoking `transformWithClause` function when check and
iterate through each CTE to verify if it is writable.

At the same time, we add comprehensive test cases to validate.

Author: hanwei

src/backend/parser/analyze.c

@@ -343,21 +343,29 @@ transformOptionalSelectInto(ParseState *pstate, Node *parseTree)
 
 			if (stmt->withClause)
 			{
-				/*
-				 * Just transform to check p_hasModifyingCTE, cte list will be transformed inside SELECT stmt.
-				 */
-				transformWithClause(pstate, stmt->withClause);
-				/*
-				 * Since Cloudberry currently only support a single writer gang, only one
-				 * writable clause is permitted per CTE. Once we get flexible gangs
-				 * with more than one writer gang we can lift this restriction.
-				 */
-				if (pstate->p_hasModifyingCTE)
-					ereport(ERROR,
-							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("writable CTE queries cannot be used with writable queries"),
-							 errdetail("Apache Cloudberry currently only support CTEs with one writable clause, called in a non-writable context."),
-							 errhint("Rewrite the query to only include one writable clause.")));
+				ListCell   *lc;
+				foreach(lc, stmt->withClause->ctes)
+				{
+					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
+					if (!IsA(cte->ctequery, SelectStmt))
+					{
+						/* must be a data-modifying statement */
+						Assert(IsA(cte->ctequery, InsertStmt) ||
+							   IsA(cte->ctequery, UpdateStmt) ||
+							   IsA(cte->ctequery, DeleteStmt));
+
+						/*
+						 * Since Cloudberry currently only support a single writer gang, only one
+						 * writable clause is permitted per CTE. Once we get flexible gangs
+						 * with more than one writer gang we can lift this restriction.
+						 */
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("writable CTE queries cannot be used with writable queries"),
+								 errdetail("Apache Cloudberry currently only support CTEs with one writable clause, called in a non-writable context."),
+								 errhint("Rewrite the query to only include one writable clause.")));
+					}
+				}
 			}
 		}
 	}

src/test/regress/expected/with.out

@@ -3264,3 +3264,76 @@ ERROR:  writable CTE queries cannot be used with writable queries
 DETAIL:  Apache Cloudberry currently only support CTEs with one writable clause, called in a non-writable context.
 HINT:  Rewrite the query to only include one writable clause.
 DROP TABLE t_w_cte_relp;
+--
+-- readable CTE with SELECT INTO clause.
+--
+WITH sel AS (
+  SELECT 1 as a
+)
+SELECT a INTO t_r_cte FROM sel;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_r_cte;
+ a 
+---
+ 1
+(1 row)
+
+DROP TABLE t_r_cte;
+--
+-- Multiple readable CTEs with SELECT INTO
+--
+WITH cte1 AS (SELECT 1 as a),
+     cte2 AS (SELECT 2 as b)
+SELECT a, b INTO t_multi_r_cte FROM cte1, cte2;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_multi_r_cte;
+ a | b 
+---+---
+ 1 | 2
+(1 row)
+
+DROP TABLE t_multi_r_cte;
+--
+-- Nested SELECT in CTE with SELECT INTO
+--
+WITH nested_cte AS (
+  SELECT * FROM (SELECT 100 as val, 'test'::text as name) subq
+)
+SELECT val, name INTO t_nested_r_cte FROM nested_cte;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_nested_r_cte;
+ val | name 
+-----+------
+ 100 | test
+(1 row)
+
+DROP TABLE t_nested_r_cte;
+--
+-- CTE with JOIN and SELECT INTO
+--
+WITH cte1 AS (SELECT 1 as id, 'foo' as val),
+     cte2 AS (SELECT 1 as id, 'bar' as val)
+SELECT cte1.id, cte1.val as val1, cte2.val as val2
+INTO t_join_r_cte
+FROM cte1 JOIN cte2 ON cte1.id = cte2.id;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_join_r_cte;
+ id | val1 | val2 
+----+------+------
+  1 | foo  | bar
+(1 row)
+
+DROP TABLE t_join_r_cte;
+--
+-- Verify mixed readable and writable CTEs blocked (negative test)
+--
+CREATE TABLE t_mixed_test (a int);
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as the Apache Cloudberry data distribution key for this table.
+HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
+WITH read_cte AS (SELECT 1 as x),
+     write_cte AS (INSERT INTO t_mixed_test VALUES (1) RETURNING *)
+SELECT x INTO t_should_fail2 FROM read_cte;  -- should fail
+ERROR:  writable CTE queries cannot be used with writable queries
+DETAIL:  Apache Cloudberry currently only support CTEs with one writable clause, called in a non-writable context.
+HINT:  Rewrite the query to only include one writable clause.
+DROP TABLE t_mixed_test;

src/test/regress/expected/with_optimizer.out

@@ -3284,3 +3284,76 @@ ERROR:  writable CTE queries cannot be used with writable queries
 DETAIL:  Apache Cloudberry currently only support CTEs with one writable clause, called in a non-writable context.
 HINT:  Rewrite the query to only include one writable clause.
 DROP TABLE t_w_cte_relp;
+--
+-- readable CTE with SELECT INTO clause.
+--
+WITH sel AS (
+  SELECT 1 as a
+)
+SELECT a INTO t_r_cte FROM sel;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_r_cte;
+ a 
+---
+ 1
+(1 row)
+
+DROP TABLE t_r_cte;
+--
+-- Multiple readable CTEs with SELECT INTO
+--
+WITH cte1 AS (SELECT 1 as a),
+     cte2 AS (SELECT 2 as b)
+SELECT a, b INTO t_multi_r_cte FROM cte1, cte2;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_multi_r_cte;
+ a | b 
+---+---
+ 1 | 2
+(1 row)
+
+DROP TABLE t_multi_r_cte;
+--
+-- Nested SELECT in CTE with SELECT INTO
+--
+WITH nested_cte AS (
+  SELECT * FROM (SELECT 100 as val, 'test'::text as name) subq
+)
+SELECT val, name INTO t_nested_r_cte FROM nested_cte;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_nested_r_cte;
+ val | name 
+-----+------
+ 100 | test
+(1 row)
+
+DROP TABLE t_nested_r_cte;
+--
+-- CTE with JOIN and SELECT INTO
+--
+WITH cte1 AS (SELECT 1 as id, 'foo' as val),
+     cte2 AS (SELECT 1 as id, 'bar' as val)
+SELECT cte1.id, cte1.val as val1, cte2.val as val2
+INTO t_join_r_cte
+FROM cte1 JOIN cte2 ON cte1.id = cte2.id;
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause. Creating a NULL policy entry.
+SELECT * FROM t_join_r_cte;
+ id | val1 | val2 
+----+------+------
+  1 | foo  | bar
+(1 row)
+
+DROP TABLE t_join_r_cte;
+--
+-- Verify mixed readable and writable CTEs blocked (negative test)
+--
+CREATE TABLE t_mixed_test (a int);
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as the Apache Cloudberry data distribution key for this table.
+HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
+WITH read_cte AS (SELECT 1 as x),
+     write_cte AS (INSERT INTO t_mixed_test VALUES (1) RETURNING *)
+SELECT x INTO t_should_fail2 FROM read_cte;  -- should fail
+ERROR:  writable CTE queries cannot be used with writable queries
+DETAIL:  Apache Cloudberry currently only support CTEs with one writable clause, called in a non-writable context.
+HINT:  Rewrite the query to only include one writable clause.
+DROP TABLE t_mixed_test;

src/test/regress/sql/with.sql

@@ -1594,3 +1594,52 @@ EXPLAIN(COSTS OFF, VERBOSE) WITH ins AS (
 )
 SELECT sum(a) INTO t_w_cte_relp_1 FROM ins;
 DROP TABLE t_w_cte_relp;
+
+--
+-- readable CTE with SELECT INTO clause.
+--
+WITH sel AS (
+  SELECT 1 as a
+)
+SELECT a INTO t_r_cte FROM sel;
+SELECT * FROM t_r_cte;
+DROP TABLE t_r_cte;
+
+--
+-- Multiple readable CTEs with SELECT INTO
+--
+WITH cte1 AS (SELECT 1 as a),
+     cte2 AS (SELECT 2 as b)
+SELECT a, b INTO t_multi_r_cte FROM cte1, cte2;
+SELECT * FROM t_multi_r_cte;
+DROP TABLE t_multi_r_cte;
+
+--
+-- Nested SELECT in CTE with SELECT INTO
+--
+WITH nested_cte AS (
+  SELECT * FROM (SELECT 100 as val, 'test'::text as name) subq
+)
+SELECT val, name INTO t_nested_r_cte FROM nested_cte;
+SELECT * FROM t_nested_r_cte;
+DROP TABLE t_nested_r_cte;
+
+--
+-- CTE with JOIN and SELECT INTO
+--
+WITH cte1 AS (SELECT 1 as id, 'foo' as val),
+     cte2 AS (SELECT 1 as id, 'bar' as val)
+SELECT cte1.id, cte1.val as val1, cte2.val as val2
+INTO t_join_r_cte
+FROM cte1 JOIN cte2 ON cte1.id = cte2.id;
+SELECT * FROM t_join_r_cte;
+DROP TABLE t_join_r_cte;
+
+--
+-- Verify mixed readable and writable CTEs blocked (negative test)
+--
+CREATE TABLE t_mixed_test (a int);
+WITH read_cte AS (SELECT 1 as x),
+     write_cte AS (INSERT INTO t_mixed_test VALUES (1) RETURNING *)
+SELECT x INTO t_should_fail2 FROM read_cte;  -- should fail
+DROP TABLE t_mixed_test;