Comments on: COUNT(*) vs COUNT(col)

By: saaj

saaj — Sun, 22 Jan 2012 12:31:12 +0000

MySQL 5.5 seems to be optimized in concern of COUNT(*) queries. At the same machine, for the table of ~120K records I’ve ~2.4 seconds for 5.1 and 0.08 seconds for 5.5 for “SELECT COUNT(*) FROM table” query.

By: muhammed sekertekin

muhammed sekertekin — Sun, 16 Oct 2011 00:48:36 +0000

very nice article i used to think that you wont notice a a difference if you use count by row i guess to have to recode a lot of my codes…. Thank you from muhammed sekertekin

By: OnLine

OnLine — Sat, 06 Aug 2011 07:06:05 +0000

Hy,
I have 2 tables.
Can I make a single Select query to return the total number of rows in the first table and the rows (their data) of the seccond table?
And if this is posible, how does this query look like?

By: Peter Zaitsev

Peter Zaitsev — Tue, 22 Mar 2011 22:51:54 +0000

Hi,

You’re looking at full index scan or full table scan in this case. Innodb has some protection from full table scan polluting cache, though it is done differently than using same page

By: Foobarista

Foobarista — Tue, 22 Mar 2011 21:21:21 +0000

In InnoDB, does a simple count(*) do anything evil with the database cache? I ask because some database engine’s I’ve seen don’t do caching carefully and tablescans (or count(*) that does a tablescan) can end up pulling the whole table into the cache (and pushing more useful pages out). Smarter db engines will just reuse the same buffer page to do table scans (after making sure it isn’t in-cache already), but many don’t.

By: Rishabh Jain

Rishabh Jain — Wed, 29 Dec 2010 07:42:07 +0000

can I use count(*)>3

By: count(*) and count(column_name) in MySQL, whatâ€™s the diff? » Eric Lo

count(*) and count(column_name) in MySQL, whatâ€™s the diff? » Eric Lo — Fri, 21 May 2010 03:29:53 +0000

[...] Performance Blog Post:COUNT(*) vs COUNT(col) Reference: [...]

By: Ilan Hazan

Ilan Hazan — Sun, 16 May 2010 12:37:24 +0000

If you need to count num results but up to a specific limit (to improve performance), you can use the Limited-Count solution.
You can read more about it here: http://www.mysqldiary.com/limited-select-count/

By: ricky

ricky — Thu, 11 Feb 2010 13:44:08 +0000

How about select count(1) vs select count(id)

Which one is better?

By: ibrahim oguz

ibrahim oguz — Sun, 31 Jan 2010 09:26:48 +0000

you say count(*) fast because it founds if there are indexes. for auto increment primary keys also is index. then if we use primary keys select count(id) from users; then it has to be fast too.
how about group by statement. nobody asked about it. select count(*) from users where country=’USA’ group by CITY;
how can we use it in innodb and myisam.
thanks.