Question

我现在搜索并尝试了很多，以便在运行此查询时弄清楚如何在表中替换名称“NULL”：

SELECT 
YEAR(orderdate) AS Years,
       (CASE WHEN country = 'US' THEN 'US' ELSE 'WORLD' END) AS region,
   SUM(netamount) AS TotSales
FROM orders o JOIN
     customers c 
     ON o.customerid = c.customerid
GROUP BY  (CASE WHEN country = 'US' THEN 'US' ELSE 'WORLD' END),YEAR(orderdate) WITH ROLLUP;

我得到这张表：http://imgur.com/pzHa8fK

我想将Null分别替换为'SubTotal''GrandTotal'。我尝试过：

COALESCE(year(orderdate), 'Subtotal') years,...

与“IFNULL（...）”相同，但不是替换名称，而是使用多年的额外列，其中所有年份再次列出并且NULL仍然存在。

有什么想法吗？

Answer 1

您可以这样做的一种方法是将查询包装在另一个选择中，然后将null值替换为COALESCE或CASE表达式：

select 
    case 
        when Years is null and region is null then 'GrandTotal'
        when Years is null then 'SubTotal' 
        else Years end Years,
    coalesce(region, '') region,
    TotSales
from
(
    SELECT YEAR(orderdate) AS Years,
       (CASE WHEN country = 'US' THEN 'US' ELSE 'WORLD' END) AS region,
       SUM(netamount) AS TotSales
    FROM orders o JOIN
         customers c 
         ON o.customerid = c.customerid
    GROUP BY  (CASE WHEN country = 'US' THEN 'US' ELSE 'WORLD' END),YEAR(orderdate) WITH ROLLUP
) d

注意，我使用CASE表达式，因为您要比较多个列。

请参阅SQL Fiddle with Demo

SQL重命名为NULL

1 个答案: