Getting the number of rows with a GROUP BY query

Question

I have a query to the effect of

SELECT t3.id, a,bunch,of,other,stuff FROM t1, t2, t3  WHERE (associate t1,t2, and t3 with each other)  GROUP BY t3.id  LIMIT 10,20 

I want to know to many total rows this query would return without the LIMIT (so I can show pagination information).

Normally, I would use this query:

SELECT COUNT(t3.id) FROM t1, t2, t3  WHERE (associate t1,t2, and t3 with each other)  GROUP BY t3.id 

However the GROUP BY changes the meaning of the COUNT, and instead I get a set of rows representing the number of unique t3.id values in each group.

Is there a way to get a count for the total number of rows when I use a GROUP BY? I'd like to avoid having to execute the entire query and just counting the number of rows, since I only need a subset of the rows because the values are paginated. I'm using MySQL 5, but I think this pretty generic.

Answer 1

There is a nice solution in MySQL.

Add the keyword SQL_CALC_FOUND_ROWS right after the keyword SELECT :

SELECT SQL_CALC_FOUND_ROWS t3.id, a,bunch,of,other,stuff FROM t1, t2, t3  WHERE (associate t1,t2, and t3 with each other)  GROUP BY t3.id  LIMIT 10,20 

After that, run another query with the function FOUND_ROWS() :

SELECT FOUND_ROWS(); 

It should return the number of rows without the LIMIT clause.

Checkout this page for more information : http://dev.mysql.com/doc/refman/5.0/en/information-functions.html#function_found-rows