union by name doesn't seem to be working correctly #15236
Description
Describe the bug
union by name seems to not be working as expected:
> create table t1 (x varchar(255), y varchar(255), z varchar(255));
0 row(s) fetched.
Elapsed 0.005 seconds.
> insert into t1 values ('a', 'b', 'c');
+-------+
| count |
+-------+
| 1 |
+-------+
1 row(s) fetched.
Elapsed 0.004 seconds.
> select t1.x, t1.y, t1.z from t1 union by name select t1.z, t1.y, t1.x, 'd' as zz from t1;
+---+---+---+------+
| x | y | z | zz |
+---+---+---+------+
| c | b | a | d |
| a | b | c | NULL |
+---+---+---+------+
2 row(s) fetched.
Elapsed 0.011 seconds.
> select x, y, z from t1 union all by name select z, y, x, 'd' as zz from t1;
+---+---+---+------+
| x | y | z | zz |
+---+---+---+------+
| a | b | c | NULL |
| c | b | a | d |
+---+---+---+------+
2 row(s) fetched.
Elapsed 0.007 seconds.The same result if using 2 tables:
> create table t2 (x varchar(255), y varchar(255), z varchar(255));
0 row(s) fetched.
Elapsed 0.004 seconds.
> insert into t2 values ('a', 'b', 'c');
+-------+
| count |
+-------+
| 1 |
+-------+
1 row(s) fetched.
Elapsed 0.003 seconds.
> select x, y, z from t1 union all by name select z, y, x, 'd' as zz from t2;
+---+---+---+------+
| x | y | z | zz |
+---+---+---+------+
| a | b | c | NULL |
| c | b | a | d |
+---+---+---+------+
2 row(s) fetched.
Elapsed 0.007 seconds.
> select x, y, z from t1 union all by name select z, y, x from t2;
+---+---+---+
| x | y | z |
+---+---+---+
| a | b | c |
| c | b | a |
+---+---+---+
2 row(s) fetched.
Elapsed 0.005 seconds.
> select x, y, z from t1 union all by name select z, y, x from t2 order by x;
+---+---+---+
| x | y | z |
+---+---+---+
| a | b | c |
| c | b | a |
+---+---+---+
2 row(s) fetched.
Elapsed 0.007 seconds.To Reproduce
See sql above.
Expected behavior
No response
Additional context
Original ticket for the feature: #14508