I believe the difference is that count(*) includes nulls (because it is counting the number of records), whereas count(column) only counts the records where the column being counted is not null, regardless of the total number of rows.
Hmm, on a related question then if I am correct above, does count(distinct column) count NULL as a distinct value or not? I.e. if I've got four records in a table with one column: (null, a, a, b), will count(distinct column) return 3 or 2? stipe42 Nic Stevens wrote: > Hi , > > This is a little off topic but I have seen count(*) on this list afew > times and it got me wondering... > > Is there a reason to use SELECT COUNT(*) as opposed to SELECT COUNT(column)? > > I have noticed that selecting count(*) versus specifying the column > name executes much more slowly. > > I've been around, on relative periphery, SQL and SQL DBMS' for a long > time but never seen count(*) used. > > These days I am more involved with SQL (using MySQL) and want to learn > more nuances as I go along. > > Cheers and thanks in advance, > > Nic > > > On 7/16/05, stipe42 <[EMAIL PROTECTED]> wrote: > >>Jack Lauman wrote: >> >>>Given the following query, how can it be modified to return 'Cuisine'(s) >>>that have no rows as having a count of zero and also return a SUM of >>>COUNT(*)? >>> >>>SELECT w.WebsiteName, r.Cuisine, COUNT(*) >>>FROM Restaurant r >>>JOIN RestaurantWebsites w >>>ON r.RestaurantID = w.RestaurantID >>>WHERE w.WebsiteName = 'TOW' >>>GROUP BY w.WebsiteName, r.Cuisine >>> >>>Thanks. >>> >>>Jack >>> >>> >> >>After the where clause tack on: >>HAVING COUNT(*)>0 >> >>This will eliminate the zero rows, but won't get you the sum. >> >>I think the only way to get the sum is to either run a second query, or >>to sum up the count column in your code as you're looping through the >>results. >> >>stipe42 >> >>-- >>MySQL General Mailing List >>For list archives: http://lists.mysql.com/mysql >>To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] >> >> > > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
