Do aliases need to have unique names in mysql union

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I've done the following, and haven't seemed to experienced any problems. Is it improper to use the same alias in different queries combined with a UNION?

SELECT table1.a,t.b,t.c
FROM table1
INNER JOIN table2 AS t ON t.table1_id=table1.id
WHERE t.fk=123
SELECT table2.a,t.b,t.c
UNION
FROM table3
INNER JOIN table4 AS t ON t.table3_id=table3.id
WHERE t.fk=123;

asked 17 secs ago

user1032531

3,460

Do aliases need to have unique names in mysql union