On Wed, Mar 19, 2008 at 1:04 PM, TG <tg-php@xxxxxxxxxxxxxxxxxxxxxx> wrote: > > It seems that count(*) pulls all the data from the row then performs a count > increment whereas count(did) only pulls the 'did' column. Again, I don't believe COUNT(*) pulls any data. If there is a row, it simply counts it. The row could be full of NULLS (if allowed by your schema - yikes) and it will still be counted. I'd guess that COUNT(1) does the same thing. COUNT(did) does only examine the `did` column, but NULL values are excluded from the count. > I wonder if count(did) is the same speed as count(1) or if it will depend on > how much/what type of data is in 'did'. > > > I also wonder why count() takes a parameter. Isn't it always going to count > +1 for the row? I'll have to look that up sometime. It takes a parameter because it depends on what you want to count. COUNT(*) will return the number of rows matching the WHERE clause. COUNT(`column_name`) will return the number of non-NULL values in the column `column_name`. You could have a million rows in the table, but if every row has NULL in `column_name`, the COUNT() will return 0. There is also COUNT(DISTINCT `column_name`), which counts the number of distinct, non-NULL values in the column. Andrew -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
