How to select from Table by group

Question

I have table like this:

idjob category customer
1560   001        1
1560   0010       1
1560   002        1
1562   001        2
1562   0010       2
1563   001        2
1563   002        3
1563   0010       3
1563   004        3

One customer can have more idjobs. Every single jobs contain a group of categories.

I would like to select the number of customer that have two or more specifics category by its jobs.

Probably it is a simple query.

How can i do that? Thank you

Answer 1

You could count the number of different idjob per customer:

SELECT   customer, GROUP_CONCAT(idjob) AS jobs
FROM     mytable
GROUP BY customer
HAVING   COUNT(DISTINCT idjob) > 1

Answer 2

You can get the customers meeting the condition using:

select customer
from t
group by customer
having min(category) <> max(category);

To get the number, use a subquery:

select count(*)
from (select customer
      from t
      group by customer
      having min(category) <> max(category)
     ) c;

Note that "2" is a special case. It can be handled by comparing the max() and min() . The more general solution would use count(distinct category) >= 2 . However, count(distinct) is more resource intensive than simpler aggregation functions.

EDIT:

Perhaps I misread the original question.

If you want customers with a particular set of categories, you can still use GROUP BY and HAVING :

select customer
from t
where category in (. . .)
group by customer
having count(*) = <n>;

Here . . . . . . is the list of categories you want. <n> is the number of categories in that list.

If you can have duplicate customer / category pairs, then use this having :

having count(distinct category) = <n>