合并 MySql 中的两行

Question

i have this query

SELECT 

CASE
WHEN bill_type = 1 THEN  
(
SELECT SUM(product_qty) FROM items
JOIN bills ON items.bill_id = bills.bill_id 
WHERE items.bill_id = i.bill_id AND items.product_id = i.product_id AND bills.bill_type = 1
LIMIT 1
)
ELSE 0
END AS input_qty,

CASE
WHEN bill_type = 2 THEN  
(
SELECT SUM(product_qty) FROM items
JOIN bills ON items.bill_id = bills.bill_id 
WHERE items.bill_id = i.bill_id AND items.product_id = i.product_id AND bills.bill_type = 2
LIMIT 1
)
ELSE 0
END AS output_qty,

stock_name,
i.product_id,
trade_name,
bill_type,
i.bill_id

FROM items i
JOIN bills b
ON i.bill_id = b.bill_id
JOIN products
ON i.product_id = products.product_id
JOIN stocks
ON b.stock_id = stocks.stock_id
GROUP BY i.product_id, b.stock_id, bill_type

and this is my output

input_qty	output_qty	item_id	bill_type	stock_id	stock_name	product_id	trade_name
200	0	43	1	1	s1	1	p1
0	150	59	2	1	s1	1	p1
200	0	18	1	2	s2	2	p2
0	150	90	2	2	s2	2	p2
650	0	18	1	2	s2	3	p3

now how can merge column with same product_id and stock_id to be like this?

input_qty	output_qty	stock_id	stock_name	product_id	trade_name
200	150	1	s1	1	p1
200	150	2	s2	2	p2
650	0	1	s2	3	p3

Answer 1

I'm pretty sure you want conditional aggregation:

SELECT p.product_id, trade_name, b.stock_id, stock_name,
      SUM(CASE WHEN bill_type = 1 THEN product_qty ELSE 0 END) as input_qty,
      SUM(CASE WHEN bill_type = 2 THEN product_qty ELSE 0 END) as output_qty
FROM items i JOIN
     bills b
     ON i.bill_id = b.bill_id JOIN
     products p
     ON i.product_id = p.product_id JOIN
     stocks s
     ON b.stock_id = s.stock_id
GROUP BY p.product_id, trade_name, b.stock_id, stock_name;

In a query that references multiple tables I strongly, strongly recommend that you qualify all column references.

Answer 2

How about removing bill_type from your GROUP BY clause, and SUM the columns you want to aggregate:

SELECT 

SUM(
CASE
WHEN bill_type = 1 THEN (SELECT SUM(product_qty) FROM items, bills WHERE items.bill_id = bills.bill_id AND bills.bill_type = 1)
ELSE 0
END) AS input_qty,

SUM(CASE
WHEN bill_type = 2 THEN (SELECT SUM(product_qty) FROM items, bills WHERE items.bill_id = bills.bill_id AND bills.bill_type = 2)
ELSE 0
END) AS output_qty,

item_id,
bill_type,
bills.stock_id,
stock_name,
items.product_id,
trade_name

FROM items
JOIN bills
ON items.bill_id = bills.bill_id
JOIN products
ON items.product_id = products.product_id
JOIN stocks
ON bills.stock_id = stocks.stock_id
GROUP BY items.product_id, bills.stock_id