MySQL更新操作的IN Criteria性能

Question

I have read that creating a temporary table is best if the number of parameters passed in the IN criteria is large. This is for select queries. Does this hold true for update queries as well ?? I have an update query which uses 3 table joins (Inner Joins) and passes 1000 parameters in the IN criteria and this query runs in a loop for 200 or more times. Which is the best approach to execute this query ?

Answer 1

IN operations are usually slow. Passing 1000 parameters to any query sounds awful. If you can avoid that, do it. Now, I'd really have a go with the temp table. You can even play with the indexing of the table. I mean, instead of just putting values in it, play with the indexes that would help you optimize your searches.

On the other hand, adding with indexes is slower that adding without indexes. Go for an empiric test there. Now, what I think is a must, bear in mind that when using the other table you don't need to use the IN clause because you can use the EXISTS clause which results usually in better performance. IE:

select * from yourTable yt
where exists (
    select * from yourTempTable ytt
    where yt.id = ytt.id
)

I don't know your query, nor data, but that would give you an idea about how to do it. Note the inner select * is as fast as select aSingleField , as the database engine optimizes it.

Those are all my thoughts. But remember, to be 100% sure of what is best for your problem, there is nothing like performing both tests and timing them :) Hope this help.