Multiple SQL queries in the same select? - mysql

Question

I am trying to combine multiple selects in one query to use as little data as possible.
I have this sql table (example)
id category status
1 test1 A
2 test2 B
3 test1 A
4 test3 B
5 test1 C
First of all i want to select how many rows there is with the same category.
SELECT category, COUNT(category) FROM test GROUP BY category
Then i would like to count the status in each category. I would do this with this query.
SELECT status, COUNT(status) FROM test WHERE category = 'test1' GROUP BY STATUS
So i want one column with total and then each categorys number of status.
Can i somehow combine these? Is that even possible or do i just have to realize that I have to get the data multiple times to have the right result?

Answer 1

You can try to GROUP BY category and by status and use WITH ROLLUP to get aggregate values:
SELECT category, status, count(*)
FROM test
GROUP BY category, status WITH ROLLUP
The result will look like this:
category | status | count(*)
----------+--------+----------
test1 | A | 2
test1 | C | 1
test1 | NULL | 3
test2 | B | 1
test2 | NULL | 1
test3 | B | 1
test3 | NULL | 1
NULL | NULL | 5
If you ignore the rows containing NULLs, the rest is the regular GROUP BY category, status. There are 2 entries having category = 'test1' AND status = 'A', one entry having category = 'test1' AND status = 'C' and so on.
The third row of the result (category = 'test1', status = NULL, count(*) = 3) summarizes the rows having category = 'test1'. It computes count(*) for all the rows having category = 'test1' no matter what value they have in column status. In a similar way there are computed the summary rows for category = 'test2' and category = 'test3'.
The last row is the summary for the entire table. count(*) = 5 includes all the rows, no matter what value they have in columns category and status.

Answer 2

You can run your second query for all categories at once like this:
mysql> select category, status, count(*) from foo group by category, status;
+----------+--------+----------+
| category | status | count(*) |
+----------+--------+----------+
| test1 | A | 2 |
| test1 | C | 1 |
| test2 | B | 1 |
| test3 | B | 1 |
+----------+--------+----------+
4 rows in set (0.39 sec)
And then you could compute the category-wide count by summing up all its rows. If you really want that too as part of the same query, you could do this:
mysql> select foo.category, status, count(*), cat_count
-> from foo
-> inner join (select category, count(*) cat_count from foo group by category) x
-> on x.category = foo.category
-> group by foo.category, status;
+----------+--------+----------+-----------+
| category | status | count(*) | cat_count |
+----------+--------+----------+-----------+
| test1 | A | 2 | 3 |
| test1 | C | 1 | 3 |
| test2 | B | 1 | 1 |
| test3 | B | 1 | 1 |
+----------+--------+----------+-----------+
4 rows in set (0.00 sec)

Answer 3

Unfortunately MySQL does not support window functions.
One way would be to get your status counts for each category in one query:
SELECT
category,
status,
COUNT(*) AS status_count
FROM
test
GROUP BY
category, status
And then INNER JOIN information about count for categories to it like that:
SELECT
a.*, b.category_count
FROM (
SELECT
category,
status,
COUNT(*) AS status_count
FROM
test
GROUP BY
category, status
) a
INNER JOIN ( SELECT category, COUNT(*) AS category_count FROM test GROUP BY category ) b ON
a.category = b.category