Mixed UNION/INTERSECT query with an explicit expression and wildcard fails with ER 1222

A mixed UNION/INTERSECT query rejects equivalent three-column projections with ER 1222 when each operand selects an explicit expression followed by a table wildcard. Explicit-column and single-operator controls return the expected row.

Steps to reproduce

1. Save the following as test.sql:

DROP DATABASE IF EXISTS set_test;

CREATE DATABASE set_test;

USE set_test;

CREATE TABLE t1 (a INT, b INT);

INSERT INTO t1 VALUES (10,20);

-- Explicit-column control.

SELECT 0 AS x, a, b FROM t1

UNION

SELECT 0 AS x, a, b FROM t1

INTERSECT

SELECT 0 AS x, a, b FROM t1;

-- UNION-only wildcard control.

SELECT 0 AS x, t1.* FROM t1

UNION

SELECT 0 AS x, t1.* FROM t1;

-- INTERSECT-only wildcard control.

SELECT 0 AS x, t1.* FROM t1

INTERSECT

SELECT 0 AS x, t1.* FROM t1;

-- Mixed-operator wildcard query.

SELECT 0 AS x, t1.* FROM t1

UNION

SELECT 0 AS x, t1.* FROM t1

INTERSECT

SELECT 0 AS x, t1.* FROM t1;

1. Run it with the MariaDB client:

mariadb < test.sql

Actual result

The first three queries each return the same three-column row:

x	a	b

0	10	20

x	a	b

0	10	20

x	a	b

0	10	20

The final mixed-operator query fails:

ERROR 1222 (21000): The used SELECT statements have a different number of columns

Expected result

The final query should also return 0,10,20. Every operand resolves to the three columns x, a, and b, just as in the explicit-column control. The set-operation precedence handling must not introduce an additional x column while expanding t1.*.

This occurs when a mixed UNION/INTERSECT chain projects both an explicit expression and a table wildcard.