mysql - 用一些字符串替换 NULL

Question

我的数据库中有一个表，如下所示:

+-------------+---------+--------+
| ProductName | Status  | Branch |
+-------------+---------+--------+
| P1          | dead    |      1 |
| P1          | dead    |      2 |
| P2          | expired |      1 |
+-------------+---------+--------+

我想将产品比较后的结果显示为:

+-------------+---------+--------+
| ProductName | Branch 1|Branch 2|
+-------------+---------+--------+
| P1          | dead    |    dead|
| P2          | expired |    OK  |
+-------------+---------+--------+

在我运行以下查询之后:

<pre>
SELECT  ProductName,
MAX(CASE 
WHEN Branch=1 
THEN Status
ELSE NULL 
END) AS 'Branch 1',
MAX(CASE 
WHEN Branch=2
THEN Status
ELSE NULL 
END) AS 'Branch 2'
FROM    MyTable
GROUP BY ProductName;

我得到的结果是:

+-------------+---------+--------+
| ProductName | Branch 1|Branch 2|
+-------------+---------+--------+
| P1          | dead    |    dead|
| P2          | expired |    NULL|  
+-------------+---------+--------+

SQLFiddle
我想用 OK 替换 NULL 但无法获得所需的结果。请指出我正确的方向。谢谢

Answer 1

使用COALESCE()转义null

SELECT  ProductName,
      COALESCE(  MAX(CASE 
            WHEN Branch=1 
            THEN Status
            ELSE NULL 
        END) ,'OK') AS 'Branch 1',
       COALESCE( MAX(CASE 
            WHEN Branch=2
            THEN Status
            ELSE NULL 
        END),'OK') AS 'Branch 2'
FROM    MyTable
GROUP BY ProductName;

DEMO