加入计数查询mysql以提高性能

Question

Have searched but can't find an answer which suits the exact needs for this mysql query.

I have the following quires on multiple tables to generate "stats" for an application:

SELECT COUNT(id) as count FROM `mod_**` WHERE `published`='1';

SELECT COUNT(id) as count FROM `mod_***` WHERE `published`='1';

SELECT COUNT(id) as count FROM `mod_****`;

SELECT COUNT(id) as count FROM `mod_*****`;

pretty simple just counts the rows sometimes based on a status.

however in the pursuit of performance i would love to get this into 1 query to save resources.

I'm using php to fetch this data with simple mysql_fetch_assoc and retrieving $res[count] if it makes a difference (pro isn't guaranteed, so plain old mysql here).

Answer 1

The overhead of sending a query and getting a single-row response is very small.

There is nothing to gain here by combining the queries.

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If you don't have indexes yet an INDEX on the published column will greatly speed up the first two queries.

Answer 2

You can use something like

SELECT SUM(published=1)

for some of that. MySQL will take the boolean result of published=1 and translate it to an integer 0 or 1 , which can be summed up.

But it looks like you're dealing with MULTIPLE tables (if that's what the ** , *** etc... are), in which case you can't really. You could use a UNION query, eg:

SELECT ...
UNION ALL
SELECT ...
UNION ALL 
SELECT ...
etc...

That can be fired off as one single query to the DB, but it'll still execute each sub-query as its own query, and simply aggregate the individual result sets into one larger set.

Answer 3

As @Halcyon said there is not much to gain here. You can anyway do several UNIONS to get all the result in one query

Answer 4

Disagreeing with @Halcyon I think there is an appreciable difference, especially if the MySQL server is on a different machine, as every single query uses at least one network packet.

I recommend you UNION the queries with a marker field to protect against the unexpected.