case表达式

 1 SELECT productid, productname, categoryid,
 2   CASE categoryid
 3     WHEN 1 THEN 'Beverages'
 4     WHEN 2 THEN 'Condiments'
 5     WHEN 3 THEN 'Confections'
 6     WHEN 4 THEN 'Dairy Products'
 7     WHEN 5 THEN 'Grains/Cereals'
 8     WHEN 6 THEN 'Meat/Poultry'
 9     WHEN 7 THEN 'Produce'
10     WHEN 8 THEN 'Seafood'
11     ELSE 'Unknown Category'
12   END AS categoryname
13 FROM Production.Products;

输出结果为：

对Sales.OrderValues视图的查询先根据val的逻辑顺序生成3个组，再把组的编号翻译成组的描述信息(Low、Medium、High)：

1 SELECT orderid, custid, val,
2   CASE NTILE(3) OVER(ORDER BY val)
3     WHEN 1 THEN 'Low'
4     WHEN 2 THEN 'Medium'
5     WHEN 3 THEN 'High'
6     ELSE 'Unknown'
7   END AS titledesc
8 FROM Sales.OrderValues
9 ORDER BY val;

查询结果如下：