case表达式

SELECT productid, productname, categoryid,
  CASE categoryid
    WHEN 1 THEN 'Beverages'
    WHEN 2 THEN 'Condiments'
    WHEN 3 THEN 'Confections'
    WHEN 4 THEN 'Dairy Products'
    WHEN 5 THEN 'Grains/Cereals'
    WHEN 6 THEN 'Meat/Poultry'
    WHEN 7 THEN 'Produce'
    WHEN 8 THEN 'Seafood'
    ELSE 'Unknown Category'
  END AS categoryname
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)：

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

查询结果如下：