mysql - MySQL - 我可以将同一张表上的多个查询组合成 1 个查询吗？

Question

我有很多查询，我可以将其合并为 1 进行优化吗？

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

我认为这应该对你有用。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

您将从查询中返回多行，全部放在一个大长列表中。

Answer 3

你可以使用：

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

Answer 4

试试这个

演示

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