MySQL - JOIN a OR b

Question

Let\'s say I have a TABLE a in which a COLUMN data is the one to join on for 2 other tables (TABLE b and TABLE

Answer 1

You can left join to both of the b and c tables, then use whichever info field is not NULL:

select coalesce(b.info, c.info) info
from a
  left join b on a.data = b.data
  left join c on a.data = c.data