How to calculate median inside a nested select query - mysql

Question

UPDATE:
My real purpose is I want to calculate a median and 3 summations all in one query. So here is what I am trying to do after suggestion
SELECT SUM(CASE WHEN i.code = 'T_186' THEN wf.value END) AS space_listed,
SUM(ws.floor_space) as floor_space_available,
SUM(ws.pallet) as pallet_space_available,
AVG(t1.value) as floor_space_median
FROM warehouses w JOIN
warehouse_factors wf
ON w.id = wf.warehouse_id JOIN
items i
ON i.id = wf.item_id JOIN
warehouse_spaces ws
ON
ws.warehouse_id=w.id LEFT JOIN
(
SELECT wf.id, wf.value, #rownum:=#rownum+1 as `row_number`, #total_rows:=#rownum
FROM (SELECT #rownum:=0) r , warehouses w
JOIN warehouse_factors wf
ON w.id=wf.id
JOIN items i
ON i.id=wf.item_id
WHERE wf.value is NOT NULL
AND
i.code = 'T_032'
ORDER BY wf.value
) as t1
ON
t1.id = w.id
WHERE i.code IN ('T_041', 'T_186', 'T_032') AND
w.city_id = 1 AND
w.stage = 'live' AND
w.warehouse_type = 'Warehouse services';
Please need help in this. I know I have to add
WHERE
t1.row_number IN ( FLOOR((#total_rows+1)/2), FLOOR((#total_rows+2)/2) );
but I can't figure how to incorporate this in the query.
Any other suggestion would be of great help

Answer 1

Two solutions (not tested, they hopefully work):
Use variables
SET
#p1 = NULL,
#p2 = NULL;
-- assign result of your first query to #p1
SELECT
#p1 := SUM(warehouse_factors.value)
FROM
...;
-- assign result of your second query to #p2
SELECT
#p2 := warehouse_factors.value
FROM
...;
SELECT
#p1 AS space_listed,
#p2 AS pallet_median;
Or:
Join both queries
SELECT
t1.space_listed,
t3.pallet_median
FROM
(
-- your first query here
) AS t1
FULL OUTER JOIN (
-- your second query here
) AS t3 ON 1 = 1

Answer 2

You seem to want conditional aggregation:
SELECT SUM(CASE WHEN i.code = 'T_186' THEN wf.value END) AS space_listed,
SUM(CASE WHEN i.code = 'T_041' AND wf.value > 0 THEN wf.value END) AS pallet_median
FROM warehouses w JOIN
warehouse_factors wf
ON w.id = wf.warehouse_id LEFT JOIN
items i
ON i.id = wf.item_id
WHERE i.code IN ('T_041', 'T_186') AND
w.city_id = 2 AND
w.stage = 'live' AND
w.warehouse_type = 'Warehouse services'