MySQL - 我可以将同一个表上的许多查询合并为一个查询吗？

Question

我有很多疑问，可以将它组合成1来优化吗？

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

I think this should work for you. It will return the 3 counts in a single SQL statement:

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 

And here is the SQL Fiddle .

Good luck.

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

You'll get back multiple rows from the queries all in one big long list.

Answer 3

你可以使用：

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

Answer 4

Try this one

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