I have a sql join 3 tables, like this:
select *
from tableA a
left join tableB b
on a.id1 = b.id1
left join tableC c
on b.id2 = c.id2
It works with the correct result, but takes so long time. For example, in each table, there is about 300 rows --> the above query takes ~ 20 seconds.
Does anyone know how to improve in this case?