Question

I’m building a MySQL query to determine how many items from each of several categories appear in a given date range. My initial attempt looked like this:

select Title,    (select count(*) from entries where CategoryID=1     and Date >= @StartDate and Date <= @EndDate) as Cat1,   (select count(*) from entries where CategoryID=2    and Date >= @StartDate and Date <= @EndDate) as Cat2,   (select count(*) from entries where CategoryID is null    and Date >= @StartDate and Date <= @EndDate) as UnkownCategory from entries   where Date >= @StartDate and Date <= @EndDate 

The table is quite large and I’d like to refactor the query to speed it up, but I’m not sure how – can this be rewritten using GROUP BY/HAVING statements or is there another way I’m missing?

Edit: Sample result set – something like this:

Title | Category 1 Total | Category 2 Total | Unknown Category Total ABC     1                  3                  0 DEF     2                  7                  2 

Answer 1

select Title, SUM(CategoryID=1) as Cat1, SUM(categoryID=2) as Cat2, SUM(categoryID IS NULL) as UnknownCategory FROM entries WHERE Date BETWEEN @StartDate AND @EndDate GROUP BY Title 

You can stick expressions in sum() functions: truth equals 1, false equals 0. Also I used the BETWEEN operator which is a little faster.

An alternative that would return a different result layout but is a little conceptually simpler:

select Title, CategoryID, count(*) from entries WHERE Date BETWEEN @StartDate AND @EndDate group by Title, CategoryID