MySQL - 我可以將同一個表上的很多查詢合併爲一個查詢嗎？

Question

我有很多疑問，我可以將它合併爲1來優化嗎？

1. SELECT COUNT(prod_id) FROM products WHERE inventory <= 5 AND cat_id = 1
2. SELECT COUNT(prod_id) FROM products WHERE inventory BETWEEN 5 AND 10 AND cat_id = 1
3. SELECT COUNT(prod_id) FROM products WHERE inventory > 10

Answer 1

我認爲這應該適合你。它將在一個SQL語句返回3個計數：

SELECT SUM(CASE WHEN inventory <= 5 AND cat_id = 1 THEN 1 ELSE 0 END) Q1Result, 
    SUM(CASE WHEN inventory BETWEEN 5 AND 10 AND cat_id = 1 THEN 1 ELSE 0 END) Q2Result, 
    SUM(CASE WHEN inventory > 10 THEN 1 ELSE 0 END) Q3Result 
FROM products 

這裏是SQL Fiddle。

祝你好運。

Answer 2

你可以使用：

select sum(x) from query 1 union query 2 etc 

Answer 3

SELECT COUNT(prod_id) FROM products WHERE inventory <= 5 AND cat_id = 1 
UNION ALL 
SELECT COUNT(prod_id) FROM products WHERE inventory BETWEEN 5 AND 10 AND cat_id = 1 
UNION ALL 
SELECT COUNT(prod_id) FROM products WHERE inventory > 10 

你會得到所有在一個大長從後面的查詢多行名單。

Answer 4

試試這個

DEMO

SELECT (
    SELECT COUNT(prod_id) FROM products WHERE inventory <= 5 AND cat_id = 1 
    ) AS count1, 
    (
    SELECT COUNT(prod_id) FROM products WHERE inventory BETWEEN 5 AND 10 AND cat_id = 1 
    ) AS count2, 
    (
    SELECT COUNT(prod_id) FROM products WHERE inventory > 10 
    ) AS count3