MySQL subquery very slow in huge table

Question

I have a sql query like this:

SELECT o_id, someColumn... FROM link_table WHERE s_id = 1 and o_id IN
(SELECT s_id FROM link_table WHERE o_id=2)

This sql query is to find out intermediate_id connected between specific s_id and o_id, but seems extremely slow. Take about 10s.

link_table is huge (with 40M rows)

Can anyone help me? Thanks.

Answer 1

Try this : As per my experience EXISTS gives better performance over IN Cluase

SELECT o_id, someColumn... 
FROM link_table t1 
WHERE s_id = 1 and EXISTS (SELECT 1 
                           FROM link_table t2 
                           WHERE t2.s_id=t1.o_id AND t2.o_id=2)

Answer 2

Try using self join:::

SELECT o_id, someColumn... FROM 
link_table A, link_table b
WHERE a.s_id = 1 AND
a.o_id=b.s_id AND
b.o_id=2