Question

I have TABLE1 as follows

+----------+----------+----------+----------+----------+
+ date     + time     + course   + runner   + position +
+----------+----------+----------+----------+----------+
+ 20120701 + 1200     + london   + aaa      +   1st    +
+ 20120701 + 1200     + london   + bbb      +   2nd    +
+ 20120701 + 1200     + london   + ccc      +   3rd    +
+ 20120701 + 1300     + london   + eee      +   1st    +
+ 20120701 + 1300     + london   + fff      +   2nd    +
+ 20120701 + 1400     + new york + ggg      +   1st    +
+ 20120701 + 1400     + new york + hhh      +   2nd    +
+ 20120702 + 2000     + london   + iii      +   1st    +
+ 20120702 + 2000     + london   + aaa      +   2nd    +
+ 20120702 + 2100     + new york + iii      +   1st    +
+ 20120702 + 2100     + new york + bbb      +   2nd    +
+----------+----------+----------+----------+----------+

and a second table

+------+----------+------+--------+--------+-----+------+-------+
+idtbl2+ date     + time + course + runner + pos + link + total +
+------+----------+------+--------+--------+-----+------+-------+
+    1 + 20120701 + 1200 + london + aaa    + 1st + WWW  +       +
+    1 + 20120701 + 1200 + london + aaa    + 1st + XXX  +       +
+    1 + 20120701 + 1200 + london + aaa    + 1st + YYY  +       +
+    1 + 20120701 + 1200 + london + aaa    + 1st + XXX  +       +
+------+----------+------+--------+--------+-----+------+-------+

Basically I need to count the number of competitors (RUNNER) in a single event from TABLE1 and update that count into the TOTAL field of the second table, TABLE2.

However, TABLE1 is 8500 records in size, and TABLE2 is 65,000 records in size. When running the following query, it timesout and loses the MySQL connection.

update table2 b, table1 a set b.total = (select count(a.runner) from table1 where a.date = b.date AND a.time = b.time AND a.course = b.course AND a.position != 'DQ'  ); 

My limited understanding of JOINs leads me to believe that a JOIN will not help with the efficiency, so I am quite stuck. Any ideas out there?

@MarkByers –

The JOIN creates a temporary table, a concatenation of both table, yes? My thinking is that no matter what, I still have to compare four fields (date, time, course, runner) from one table against another.

I tried this, but it also times out:

Answer 1

1. Remove table1 from the update clause, as you are already joining the tables (internally) with the nested Select count…. You are joining table2 and table1 without a where clause, the resulting product is so big to be processed that your engine times out.

2. Check the where clause in the nested select, I think you should filter the query by Runner, otherwise you are counting different Runners that have the same time, date, course, etc; unless that is what you want.

update table2 b
set b.total = (select count(a.runner) 
      from table1 
      where a.date = b.date 
      AND a.time = b.time 
      AND a.course = b.course 
      AND a.position != 'DQ'  
      AND b.runner = a.runner);