Re: Efficient way to count rows when using GROUP BY

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It worked!

SELECT COUNT(*) FROM (SELECT COUNT(*) FROM ad.off_enrol GROUP BY jcu_campus, sub_code) t1

Thank you list -:)

Martín Marqués wrote:

El Dom 26 Jun 2005 07:39, Ross Honniball escribió:
Hi All,

I use
SELECT COUNT(*) FROM whatever WHERE whatever

to determine how many rows a particular query will return (then use this
count to assist with pagination).
The problem is that this does not work if the query contains a GROUP BY
statement as, of course,
the query will return many rows each with a count by each grouping.

Does anyone know an efficient way to determine the number of ROWS a query
with a GROUP BY
statement will return (without just executing the entire query with no LIMIT
statement)?

You are not stating which database you are working with, but I would do this (don't know if it's efficient, but it'll work):

SELECT sum(count) FROM (SELECT COUNT(*) AS count FROM whatever WHERE whatever) t1;

Hope it helps.


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