每個派生的表必須有自己的別名錯誤在MySQL

Question

我有以下查詢：

SELECT SUM(cost) 
FROM (

SELECT s.cost 
FROM sandwiches AS s 
WHERE s.name = "Cheese Steak" 
) 
UNION (

SELECT p.cost 
FROM pizza AS p 
WHERE TYPE = "Plain" 
AND SIZE = "L" 
) 

這給了我一個錯誤：

＃1248 - 每一個派生表必須有自己的別名

Answer 1

你需要你的別名臨時表

SELECT SUM(cost) 
FROM 
(
    (
    SELECT s.cost 
    FROM sandwiches AS s 
    WHERE s.name = "Cheese Steak" 
) AS T1 
UNION 
    (
    SELECT p.cost 
    FROM pizza AS p 
    WHERE TYPE = "Plain" 
    AND SIZE = "L" 
) AS T2 
) AS T 

Answer 2

你想要整個Sum嗎？

SELECT 
    (SELECT SUM(s.cost) 
    FROM sandwiches AS s 
    WHERE s.name = "Cheese Steak" 
) 
+ 
    (SELECT SUM(p.cost) 
    FROM pizza AS p 
    WHERE p.TYPE = "Plain" 
     AND p.SIZE = "L" 
) 

Answer 3

下面的表格應該做的工作：

SELECT SUM(cost) FROM (
    SELECT cost FROM sandwiches WHERE name = "Cheese Steak" 
    UNION 
    SELECT cost FROM pizza WHERE TYPE = "Plain" AND SIZE = "L" 
) as temp 

MySQL只需要子選擇一個臨時表名。