Count data from multiple tables using SUM - mysql

Question

I have table with positions
tbl_positions
id position
1 Driver
2 Lobby
3 Support
4 Constructor
and in other table i have users
EDIT:
tbl_workers
id name position position2 status
1 John 2 3 4
2 Mike 3 2 2
3 Kate 2 0 3
4 Andy 1 0 0
i do request of positions
SELECT p.id,
p.position,
SUM(CASE w.Status WHEN 2 THEN 1 ELSE 0 END) AS booked,
SUM(CASE w.Status WHEN 3 THEN 1 ELSE 0 END) AS placed
FROM tbl_positions AS p LEFT JOIN tbl_workers AS w
ON w.position=p.id
GROUP BY p.id, p.position
I need output like this in single query.
Position booked placed
Driver 0 0
Lobby 1 2
Support 0 2
Constructor 0 0
I need to evalate both field positon1 and position2 instead of one. I think its easy to modify it but i cannot find the right solution please help.
EDIT : Added status 4

Answer 1

Instead of joining to tbl_workers you could join to its unpivoted variation where position and position2 would be in the same column but in different rows.
Here's how the unpivoting might look like:
SELECT
w.id,
w.name,
CASE x.pos WHEN 1 THEN w.position ELSE w.position2 END AS position,
w.status
FROM tbl_workers AS w
CROSS JOIN (SELECT 1 AS pos UNION ALL SELECT 2) AS x
Here's the entire query, which is basically your original query with the above query substituting for the tbl_workers table:
SELECT p.id,
p.position,
SUM(CASE w.Status WHEN 2 THEN 1 ELSE 0 END) AS booked,
SUM(CASE w.Status WHEN 3 THEN 1 ELSE 0 END) AS placed
FROM tbl_positions AS p
LEFT JOIN (
SELECT
w.id,
w.name,
CASE x.pos WHEN 1 THEN w.position ELSE w.position2 END AS position,
w.status
FROM tbl_workers AS w
CROSS JOIN (SELECT 1 AS pos UNION ALL SELECT 2) AS x
) AS w
ON w.position=p.id
GROUP BY p.id, p.position
UPDATE
This is a modified script according to additional request in comments:
SELECT p.id,
p.position,
SUM(CASE w.Status WHEN 2 THEN 1 ELSE 0 END) AS booked,
SUM(CASE w.Status WHEN 3 THEN 1 ELSE 0 END) AS placed
FROM tbl_positions AS p
LEFT JOIN (
SELECT
w.id,
w.name,
CASE x.pos WHEN 1 THEN w.position ELSE w.position2 END AS position,
CASE w.status
WHEN 4 THEN CASE x.pos WHEN 1 THEN 3 ELSE 2 END
ELSE w.status
END AS status
FROM tbl_workers AS w
CROSS JOIN (SELECT 1 AS pos UNION ALL SELECT 2) AS x
) AS w
ON w.position=p.id
GROUP BY p.id, p.position
The idea is to substitute the 4 status in the subselect with 3 or 2 depending on whether we are currently to pull position or position2 as the unified position. The outer select keeps using the same logic as before.

Answer 2

not really sure what you mean by "evaluate both fields" - but here is an example on how to sum up both:
SELECT
P.ID,
P.POSITION,
((SELECT SUM (CASE W.STATUS WHEN 2 THEN 1 ELSE 0 END) FROM TBL_WORKERS W WHERE W.POSITION = P.ID) + (SELECT SUM (CASE W.STATUS WHEN 2 THEN 1 ELSE 0 END) FROM TBL_WORKERS W WHERE W.POSITION2 = P.ID)) AS BOOKED,
((SELECT SUM (CASE W.STATUS WHEN 3 THEN 1 ELSE 0 END) FROM TBL_WORKERS W WHERE W.POSITION = P.ID) + (SELECT SUM (CASE W.STATUS WHEN 3 THEN 1 ELSE 0 END) FROM TBL_WORKERS W WHERE W.POSITION2 = P.ID)) AS PLACED
FROM TBL_POSITIONS P

Answer 3

since your data is not normalized (ie: two columns both representing a position in a single row), I would do a UNION of the workers first, then apply your outer count/group by... something like... Each part of the inner query is pre-aggregating and only counting for the records qualifying the status 2 or 3 and have a position. So, if you have a large table, it would be more noticeable for performance. Then, that result gets summed at the outer level for all possible positions using COALESCE() to prevent NULL values in your output result.
SELECT
p.id,
p.position,
coalesce( SUM(w.Booked), 0 ) AS booked,
coalesce( SUM(w.Placed), 0 ) AS placed
FROM
tbl_positions AS p
LEFT JOIN
( select w1.Position as PositionID,
sum( if( w1.status = 2, 1, 0 )) as Booked,
sum( if( w1.status = 3, 1, 0 )) as Placed
from
tbl_workers w1
where
w1.status in ( 2, 3 )
and w1.Position > 0
group by
PositionID
union all
select w2.Position2 as PositionID,
sum( if( w2.status = 2, 1, 0 )) as Booked,
sum( if( w2.status = 3, 1, 0 )) as Placed
from
tbl_workers w2
where
w2.status in ( 2, 3 )
and w2.Position2 > 0
group by
PositionID ) as w
on p.id = w.positionID
group by
p.id,
p.position