Question

I’m currently working on writing report generators. For one report I need to do a breakdown by a given characteristic (supplier, logging user, language, etc which for each row includes the name of the characteristic I’m interested in, the number of items that match that characterastic, and the percentage of total items this figure represents. The first two aren’t a problem, the third is.

For example, to get a breakdown by language I’d be using a query like this.

SELECT lang_id, 
COUNT(IF(open=TRUE,1,NULL)) AS lang_total
FROM table
GROUP BY lang_id;

This gives me the number of items per language.

I can get the total number of items in the table and store it in a variable simply enough with a plain count.

SELECT @totalOpen:=COUNT(*) FROM table WHERE open = TRUE;

Now I want to add a third column, which is the figure in lang_total divided by the value in @totalOpen multiplied by 100 (in other words, the percentage of all items that fit the criteria). Something along the lines of the following:

This is the bit I’m having trouble with, as because as far as I can tell you can’t use aggregate columns in calculations.

SELECT lang_id, 
COUNT(IF(open=true,1,NULL)) AS lang_total
(lang_total/@totalOpen)*100 as lang_percent
FROM table
GROUP BY lang_id;

I’m sure that there must be a way of doing this in MySQL, but I’ve not been able to track it down. Can anyone help out with this?

Answer 1

I read this question now for the first time. I know that probably it’s too late to be useful for you but I would have solved in this way.

select lang_id, 
sum(if(open= true,1,0)) as lang_total,
coalesce(sum(if(open= true,1,null)) / @r,0) as percentage
from table,(select @r:=count(*) from table where open = TRUE) as t
group by lang_id;