Comments on: count(1) vs count(*) – any difference? http://www.rustyrazorblade.com/2007/01/count1-vs-count-any-difference/ Tech Thoughts, Mostly on LAMP - by Jon Haddad Fri, 03 Sep 2010 03:50:22 -0700 http://wordpress.org/?v=2.8.4 hourly 1 By: Jay Pipes http://www.rustyrazorblade.com/2007/01/count1-vs-count-any-difference/comment-page-1/#comment-3682 Jay Pipes Thu, 25 Jan 2007 03:35:58 +0000 http://www.rustyrazorblade.com/index.php/2007/01/19/count1-vs-count-any-difference/#comment-3682 Hi! They are identical in MSSQL as well. There is, however, a big difference in T-SQL/MSSQL between the performance of EXISTS() and SELECT COUNT(*) to determine existence... Cheers, Jay Hi!

They are identical in MSSQL as well. There is, however, a big difference in T-SQL/MSSQL between the performance of EXISTS() and SELECT COUNT(*) to determine existence…

Cheers,

Jay

]]> By: Philip Stoev http://www.rustyrazorblade.com/2007/01/count1-vs-count-any-difference/comment-page-1/#comment-3633 Philip Stoev Sun, 21 Jan 2007 15:40:17 +0000 http://www.rustyrazorblade.com/index.php/2007/01/19/count1-vs-count-any-difference/#comment-3633 COUNT(*) is converted to COUNT(1) within the parser, therefore very early in the query execution sequence. COUNT(*) is converted to COUNT(1) within the parser, therefore very early in the query execution sequence.

]]> By: Kevin Burton http://www.rustyrazorblade.com/2007/01/count1-vs-count-any-difference/comment-page-1/#comment-3620 Kevin Burton Sat, 20 Jan 2007 06:05:36 +0000 http://www.rustyrazorblade.com/index.php/2007/01/19/count1-vs-count-any-difference/#comment-3620 Also, on MyISAM an internal row count is maintained which is used for COUNT...... Also, on MyISAM an internal row count is maintained which is used for COUNT……

]]> By: Ed http://www.rustyrazorblade.com/2007/01/count1-vs-count-any-difference/comment-page-1/#comment-3608 Ed Fri, 19 Jan 2007 16:25:42 +0000 http://www.rustyrazorblade.com/index.php/2007/01/19/count1-vs-count-any-difference/#comment-3608 They are treated essentially the same. You can see below that mysql internally rewrites count(*) to count(0). mysql> explain extended select count(*) from foo; +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ 1 row in set, 1 warning (0.03 sec) mysql> show warnings; +-------+------+-------------------------------------------------+ | Level | Code | Message | +-------+------+-------------------------------------------------+ | Note | 1003 | select count(0) AS `count(*)` from `test`.`foo` | +-------+------+-------------------------------------------------+ 1 row in set (0.00 sec) mysql> explain extended select count(1) from foo; +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> show warnings; +-------+------+-------------------------------------------------+ | Level | Code | Message | +-------+------+-------------------------------------------------+ | Note | 1003 | select count(1) AS `count(1)` from `test`.`foo` | +-------+------+-------------------------------------------------+ 1 row in set (0.00 sec) They are treated essentially the same. You can see below that mysql internally rewrites count(*) to count(0).

mysql> explain extended select count(*) from foo;
+—-+————-+——-+——+—————+——+———+——+——+——————————+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+—-+————-+——-+——+—————+——+———+——+——+——————————+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away |
+—-+————-+——-+——+—————+——+———+——+——+——————————+
1 row in set, 1 warning (0.03 sec)

mysql> show warnings;
+——-+——+————————————————-+
| Level | Code | Message |
+——-+——+————————————————-+
| Note | 1003 | select count(0) AS `count(*)` from `test`.`foo` |
+——-+——+————————————————-+
1 row in set (0.00 sec)

mysql> explain extended select count(1) from foo;
+—-+————-+——-+——+—————+——+———+——+——+——————————+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+—-+————-+——-+——+—————+——+———+——+——+——————————+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away |
+—-+————-+——-+——+—————+——+———+——+——+——————————+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+——-+——+————————————————-+
| Level | Code | Message |
+——-+——+————————————————-+
| Note | 1003 | select count(1) AS `count(1)` from `test`.`foo` |
+——-+——+————————————————-+
1 row in set (0.00 sec)

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