Question

我有很多疑问，可以将它合并为1进行优化吗？

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

Answer 1

我认为这对你有用。它将在单个SQL语句中返回3个计数：

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

这是SQL Fiddle。

祝你好运。

Answer 2

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

您将从一个很长的列表中的所有查询中获取多行。

Answer 3

您可以使用：

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

Answer 4

试试这个

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

MySQL - 我可以将同一个表上的许多查询合并为一个查询吗？

4 个答案: