why are subqueries so slow? Is this because their implementation is still not optimized? Take for example the following queries and have a look at the timing:
mysql> select wordid from words where val = 'henning'; +--------+ | wordid | +--------+ | 144005 | +--------+ 1 row in set (0.00 sec)
mysql> select count(*) from wordlist where wordid in (select wordid from words where val = 'henning');
+----------+
| count(*) |
+----------+
| 55 |
+----------+
1 row in set (0.88 sec)
mysql> select count(*) from wordlist where wordid in (144005); +----------+ | count(*) | +----------+ | 55 | +----------+ 1 row in set (0.00 sec)
I did more tests and observed a constant time factor around 1 sec that is introduced
by using subqueries. I depend on those queries running fast and if I have a 0.88 sec
overhead it will sum up quickly. So for now, I either use local code to do the query
first and insert the value manually or use a join.
Bottom line: I would really love to use subqueries but something seems not right.
Andreas Pardeike
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