Question

我在SALES表中有以下数据：

Customer   Year   Amount'
 1         2011     1500
 1         2012     2000
 1         2013     1900
 2         2011     4500
 2         2012     5000
 2         2013     6000

使用以下查询：

SELECT * FROM SALES WHERE Year=2012 
UNION
SELECT * FROM SALES WHERE Year=2013

我得到了这个结果：

Customer  Year  Amount
1         2012  2000
1         2013  1900
2         2012  5000
2         2013  6000

但是，现在我的问题是：我应该如何编写查询以获得如下结果？

Customer  Amount2012 Amount2013
1         2000        1900
2         5000        6000

Answer 1

您不需要使用UNION来编写两个条件，您可以使用IN谓词或WHERE Year = 2012 OR Year = 2013执行此操作，然后使用CASE表达式将每年的金额放在一个单独的栏目中：

SELECT
  Customer,
  MAX(CASE WHEN Year = 2012 THEN Amount ELSE 0 END) AS Amount2012,
  MAX(CASE WHEN Year = 2013 THEN Amount ELSE 0 END) AS Amount2013
FROM SALES 
WHERE Year IN(2012, 2013)
GROUP BY Customer;

或者，您可以使用PIVOT表运算符将金额的行数转换为列，如下所示：

SELECT
  Customer,
  [2012] AS Amount2012,
  [2013] AS Amount2013
FROM
(
  SELECT *
  FROM Sales 
  WHERE Year IN(2012, 2013)
) AS t
PIVOT
(
  MAX(Amount)
  FOR Year IN([2012], [2013])
) AS p;

SQL Fiddle Demo

这会给你：

╔═══════════╦═════════════╦════════════╗
║ CUSTOMER  ║ AMOUNT2012  ║ AMOUNT2013 ║
╠═══════════╬═════════════╬════════════╣
║        1  ║       2000  ║       1900 ║
║        2  ║       5000  ║       6000 ║
╚═══════════╩═════════════╩════════════╝

Answer 2

试试这个

SELECT Customer,
       SUM(CASE WHEN Year=2012 then Amount else 0 END) Amoumt2012,
       SUM(CASE WHEN Year=2013 then Amount else 0 END) Amoumt2013
FROM SALES WHERE Year in (2012 ,2013)
GROUP BY Customer

从WHERE子句筛选的两列中的同一表中返回数据

2 个答案: