Question

我想创建一个将连接用户的全名的视图。如果用户具有扩展名，则会将其与全名连接。

例如：

John May Brown（Fname，Mname，Lname）

，扩展名为

John May Brown Jr.（Fname，Mname，Lname，ExtName）

我的代码：

Create view viewforum (
  SELECT A.*, CONCAT(B.Fname," ",B.Mname," ",B.Lname," ",B.ExtName) AS Fullname
  FROM forum_table A INNER JOIN user_table B
  WHERE A.user_id = B.user_id
);

输出：

Fullname列下的所有数据均为NULL，因为某些用户信息上没有扩展名。所以输出是NULL。

我如何制定条件？

Answer 1

为了消除nulls：

，有点复杂

Create view viewforum (SELECT A.*, 
   CONCAT(
        B.Fname,
        " ",
        COALESCE(B.Mname, ""),
        " ",
        B.Lname," ",
        COALESCE(B.ExtName,"")
   ) AS Fullname FROM forum_table A INNER JOIN user_table B WHERE A.user_id = B.user_id);

COALESCE将从值列表中选择第一个非空值。如果COALESCE(B.ExtName, "")为B.ExtName

，则Null会产生空字符串

Answer 2

您可以使用IFNULL来处理空值

Create view viewforum 
(  SELECT A.*, CONCAT(IFNULL(B.Fname," "),"  ",IFNULL(B.Mname," ")," ",IFNULL(B.Lname," ")," ",IFNULL(B.ExtName," ")) AS Fullname
FROM forum_table A INNER JOIN user_table B
WHERE A.user_id = B.user_id
);

将返回没有空问题的所需结果

如何使用扩展名来连接fullname？

2 个答案: