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GROUP BY并在MySQL中仅显示非空列值

2024-04-20 21:52:03 324

让我们首先创建一个表-

mysql> create table DemoTable
   -> (
   -> Id varchar(100),
   -> Message varchar(200)
   -> );

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable values('1','');

mysql> insert into DemoTable values('1','Hi');

mysql> insert into DemoTable values('2','Hello');

mysql> insert into DemoTable values('3','Awesome');

mysql> insert into DemoTable values('3','Good Morning');

mysql> insert into DemoTable values('2',NULL);

使用select语句显示表中的所有记录-

mysql> select *from DemoTable;

输出结果

+------+--------------+
| Id   | Message      |
+------+--------------+
| 1    |              |
| 1    | Hi           |
| 2    | Hello        |
| 3    | Awesome      |
| 3    | Good Morning |
| 2    | NULL         |
+------+--------------+
6 rows in set (0.00 sec)

以下是用于分组并选择第一个非空列的查询-

mysql> select Id,min(Message) from DemoTable
   -> where Message IS NOT NULL and  length(Message) > 0
   -> group by Id;

输出结果

+------+--------------+
| Id   | min(Message) |
+------+--------------+
| 1    | Hi           |
| 2    | Hello        |
| 3    | Awesome      |
+------+--------------+
3 rows in set (0.06 sec)

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GROUP BY并在MySQL中仅显示非空列值

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