选择（选择联盟的所有选择）错误

Question

有什么不对这个查询：

SELECT AVG(price) as AVG_price FROM 
(
(SELECT price FROM PC, Product WHERE maker = 'A' AND Product.model = PC.model) 
    UNION ALL 
(SELECT price FROM Laptop, Product WHERE maker = 'A' AND Product.model = Laptop.model) 
) 

它提供了以下错误：

Incorrect syntax near ')'

Answer 1

试试这个..

SELECT AVG(d.price) as AVG_price FROM 
(
SELECT price FROM PC, Product WHERE maker = 'A' AND Product.model = PC.model 
    UNION ALL 
SELECT price FROM Laptop, Product WHERE maker = 'A' AND Product.model = Laptop.model 
) as d 

Answer 2

请尝试这种语法。

SELECT AVG(price) as AVG_price FROM 
(
    (SELECT price FROM PC, Product WHERE maker = 'A' AND Product.model = PC.model) 
    UNION ALL 
    (SELECT price FROM Laptop, Product WHERE maker = 'A' AND Product.model = Laptop.model) 
) AS ALIAS_NAME 

我在查询结尾添加了ALIAS_NAME。这可以解决你的问题。

Answer 3

我认为你需要给内联表的别名

SELECT AVG(price) as AVG_price FROM 
(
    (SELECT price FROM PC, Product WHERE maker = 'A' AND Product.model = PC.model) 
     UNION ALL 
    (SELECT price FROM Laptop, Product WHERE maker = 'A' AND Product.model = Laptop.model) 
) tableAlias 

应该做的伎俩

Answer 4

别名派生表，并转换为SQL-92 ANSI标准。

SELECT AVG(price) as AVG_price FROM 
(
SELECT price FROM PC INNER JOIN Product on Product.model = PC.model 
WHERE maker = 'A' 
    UNION ALL 
SELECT price FROM Laptop INNER JOIN Product on Product.model = Laptop.model 
WHERE maker = 'A' 
) B 

Answer 5

随着现代风格JOIN S：

SELECT AVG(price) 
FROM 
(
SELECT price 
FROM PC JOIN Product ON Product.model = PC.model 
WHERE maker = 'A' 

UNION ALL 

SELECT price 
FROM Laptop JOIN Product ON Product.model = Laptop.model 
WHERE maker = 'A' 
) as dt