[英]How to combine two sql queries?
I have a stock table and I would like to create a report that will show how often were items ordered. 我有一个库存表,我想创建一个报告,显示订购商品的频率。
"stock" table: “股票”表:
item_id | pcs | operation
apples | 100 | order
oranges | 50 | order
apples | -100 | delivery
pears | 100 | order
oranges | -40 | delivery
apples | 50 | order
apples | 50 | delivery
Basically I need to join these two queries together. 基本上我需要将这两个查询连接在一起。
A query which prints stock balances: 打印库存余额的查询:
SELECT stock.item_id, Sum(stock.pcs) AS stock_balance
FROM stock
GROUP BY stock.item_id;
A query which prints sales statistics 打印销售统计信息的查询
SELECT stock.item_id, Sum(stock.pcs) AS pcs_ordered, Count(stock.item_id) AS number_of_orders
FROM stock
GROUP BY stock.item_id, stock.operation
HAVING stock.operation="order";
I think that some sort of JOIN would do the job but I have no idea how to glue queries together. 我认为某种JOIN可以完成这项工作,但我不知道如何将查询粘合在一起。
Desired output: 期望的输出:
item_id | stock_balance | pcs_ordered | number_of_orders
apples | 0 | 150 | 2
oranges | 10 | 50 | 1
pears | 100 | 100 | 1
This is just example. 这只是一个例子。 Maybe, I will need to add more conditions because there is more columns. 也许,我需要添加更多条件,因为有更多列。 Is there a universal technique of combining multiple queries together? 是否存在将多个查询组合在一起的通用技术?
SELECT a.item_id, a.stock_balance, b.pcs_ordered, b.number_of_orders
FROM
(SELECT stock.item_id, Sum(stock.pcs) AS stock_balance
FROM stock
GROUP BY stock.item_id) a
LEFT OUTER JOIN
(SELECT stock.item_id, Sum(stock.pcs) AS pcs_ordered,
Count(stock.item_id) AS number_of_orders
FROM stock
WHERE stock.operation = "order"
GROUP BY stock.item_id) b
ON a.item_id = b.item_id
This should do it 这应该做到这一点
SELECT
stock.item_id,
Sum(stock.pcs) AS stock_balance,
pcs_ordered,
number_of_orders
FROM stock LEFT OUTER JOIN (
SELECT stock.item_id,
SUM(stock.pcs) AS pcs_ordered,
COUNT(stock.item_id) AS number_of_orders
FROM stock
WHERE stock.operation ='order'
GROUP BY stock.item_id
) s2 ON stock.item_id = s2.item_id
GROUP BY
stock.item_id,
pcs_ordered,
number_of_orders
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