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MySQL查询将两列合并为一个列？

2024-05-17 03:40:05 380

您可以COALESCE()为此使用功能。在该COALESCE()函数中，它从列中返回第一个NONNULL值。为了理解这个概念，让我们首先创建一个演示表

mysql> create table combineTwoColumnsDemo
   -> (
   -> UserId int,
   -> UserName varchar(20),
   -> UserAge int
   -> );

使用insert命令在表中插入一些记录。查询如下-

mysql> insert into combineTwoColumnsDemo values(101,'John',23);
mysql> insert into combineTwoColumnsDemo values(102,'Carol',20);
mysql> insert into combineTwoColumnsDemo values(103,'Bob',25);
mysql> insert into combineTwoColumnsDemo values(104,'Mike',26);
mysql> insert into combineTwoColumnsDemo values(105,NULL,23);
mysql> insert into combineTwoColumnsDemo values(105,'Maxwell',NULL);

现在，您可以使用select语句显示表中的所有记录。查询如下-

mysql> select *from combineTwoColumnsDemo;

以下是输出

+--------+----------+---------+
| UserId | UserName | UserAge |
+--------+----------+---------+
|    101 | John     |      23 |
|    102 | Carol    |      20 |
|    103 | Bob      |      25 |
|    104 | Mike     |      26 |
|    105 | NULL     |      23 |
|    105 | Maxwell  |    NULL |
+--------+----------+---------+
6 rows in set (0.00 sec)

这是将两列合并为一个查询的查询

mysql> SELECT UserName,
   -> UserAge,
   -> COALESCE(UserName, UserAge) AS Combine_UserName_UserAge
   -> FROM combineTwoColumnsDemo;

以下是输出

+----------+---------+--------------------------+
| UserName | UserAge | Combine_UserName_UserAge |
+----------+---------+--------------------------+
| John     |      23 | John                     |
| Carol    |      20 | Carol                    |
| Bob      |      25 | Bob                      |
| Mike     |      26 | Mike                     |
| NULL     |      23 | 23                       |
| Maxwell  |    NULL | Maxwell                  |
+----------+---------+--------------------------+
6 rows in set (0.00 sec)

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MySQL查询将两列合并为一个列？

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