How to get data from 2 different tables and with different fields?

Question

MySQL

for example 2 tables
t1 (id_user, user_name)
t2 (id_article, description, content,)
UINION ALL does not work - different number of columns.

Answer 1

you need to equalize the number of fields in the selections, for example

SELECT t1. id_user, t1.user_name, NULL
FROM t1
UNION ALL
t2.id_article, t2.description, t2.content
FROM t2

some engines may require explicit casting in this case.