How can I speed up MySQL query with multiple joins

Question

Here is my issue, I am selecting and doing multiple joins to get the correct items...it pulls in a fair amount of rows, above 100,000. This query takes more than 5mins when the

Answer 1

I'd try the following:

First, ensure there are indexes on the following tables and columns (each set of columns in parentheses should be a separate index):

table1 : (subscribe, CDate)
         (CU_id)
table2 : (O_cid)
         (O_ref)
table3 : (I_oref)
         (I_pid)
table4 : (P_id)
         (P_cat)
table5 : (C_id, store)

Second, if adding the above indexes didn't improve things as much as you'd like, try rewriting the query as

SELECT DISTINCT t1.first_name, t1.last_name, t1.email FROM
  (SELECT CU_id, t1.first_name, t1.last_name, t1.email
     FROM table1
     WHERE subscribe = 1 AND
           CDate >= $startDate AND
           CDate <= $endDate) AS t1
  INNER JOIN table2 AS t2
    ON t1.CU_id = t2.O_cid   
  INNER JOIN table3 AS t3
    ON t2.O_ref = t3.I_oref   
  INNER JOIN table4 AS t4
    ON t3.I_pid = t4.P_id   
  INNER JOIN (SELECT C_id FROM table5 WHERE store = 2) AS t5
    ON t4.P_cat = t5.C_id

I'm hoping here that the first sub-select would cut down significantly on the number of rows to be considered for joining, hopefully making the subsequent joins do less work. Ditto the reasoning behind the second sub-select on table5.

In any case, mess with it. I mean, ultimately it's just a SELECT - you can't really hurt anything with it. Examine the plans that are generated by each different permutation and try to figure out what's good or bad about each.

Share and enjoy.