MySQL - Multi-threaded Update (no thread updates the same id) but having Deadlock

Question

I have a multi threaded java program that is running update statements on my MySQL DB. When I use threads I get deadlock although I am never updating the same rows in any two threads. For each time this query is ran field_a is different so why would I have lock issues?

thread1: field_a - 'A'
thread2: field_a - 'B'
thread3: field_a - 'C'

I am running a query like this

 UPDATE table as t, 
            (
             SELECT field_a,
                   field_b,
                   TRUNCATE(AVG(Sumfield_c), 2) avgfield_c,
                   TRUNCATE(AVG(Sumfield_d), 2) avgfield_d
             FROM
              (SELECT field_a,
                      field_b,
                      DateString,
                      sum(field_c) Sumfield_c,
                      sum(field_d) Sumfield_d
               FROM table
               WHERE DateString > DATE_FORMAT(SUBDATE(CURDATE(), 22), '%Y%m%d') and field_a = ? and id <= ?
               GROUP BY field_a,
               field_b,
                        DateString) A
             GROUP BY field_a,
                     field_b
            ) as temp
             SET t.Avgfield_c = temp.avgfield_c, t.Avgfield_d = temp.avgfield_d WHERE t.field_a = temp.field_a and t.field_b = temp.field_b and t.id > ?;

Answer 1

After hours and hours I got it working by creating a new index.

CREATE INDEX newIndex ON table (fieldA, fieldB);

Hope this helps someone in the future running a similar query with threading.