NYCPHP Meetup

[nycphp-talk] Re: MySQL doubt

Faber Fedor faber at linuxnj.com
Fri Jan 14 09:31:39 EST 2005


On 14/01/05 00:43 -0500, Adam Fields wrote:
> This won't show anything different

Looks different to me:

mysql> explain select count(*) from foobar  ;
+------------------------------+
| Comment                      |
+------------------------------+
| Select tables optimized away |
+------------------------------+
1 row in set (0.01 sec)

mysql> explain select count(row_names) from r1000g_meanVectors  ;
+--------------------+------+---------------+------+---------+------+------+-------+
| table  | type | possible_keys | key  | key_len | ref  | rows | Extra |
+--------------------+------+---------------+------+---------+------+------+-------+
| foobar | ALL  | NULL          | NULL |    NULL | NULL | 149 |       |
+--------------------+------+---------------+------+---------+------+------+-------+
1 row in set (0.01 sec)

> I hope that it would optimize this to reading off an internal row
> counter rather than fetching all of the rows and counting them. In the
> former case, they should be the same. If it's doing the latter,
> count(field) will be faster.

The first one in my example says to me "I don't even need to look at the
table, I already know the answer" and the second one tells me the table
has to be looked at.


-- 
 
Regards,
 
Faber                     

Linux New Jersey: Open Source Solutions for New Jersey
http://www.linuxnj.com






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