MySQL 如何将不同查询结果合并成一个字符串

使用MySQL的group_concat()函数进行连接。先创建一个表 –

mysql> create table DemoTable
   -> (
   -> Subject varchar(10)
   -> );
Query OK, 0 rows affected (0.43 sec)

使用insert命令向表格插入一些记录 –

mysql> insert into DemoTable values('C');
Query OK, 1 row affected (0.20 sec)

mysql> insert into DemoTable values('C++');
Query OK, 1 row affected (0.25 sec)

mysql> insert into DemoTable values('C++');
Query OK, 1 row affected (0.06 sec)

mysql> insert into DemoTable values('MongoDB');
Query OK, 1 row affected (0.17 sec)

mysql> insert into DemoTable values('MySQL');
Query OK, 1 row affected (0.14 sec)

mysql> insert into DemoTable values('MongoDB');
Query OK, 1 row affected (0.14 sec)

mysql> insert into DemoTable values('MongoDB');
Query OK, 1 row affected (0.34 sec)

mysql> insert into DemoTable values('Java');
Query OK, 1 row affected (0.18 sec)

mysql> insert into DemoTable values('Java');
Query OK, 1 row affected (0.10 sec)

使用select语句显示表格中的所有记录：

mysql> select *from DemoTable;

阅读更多：MySQL 教程

输出

这将产生以下输出 –

+---------+
| Subject |
+---------+
| C       |
| C++     |
| C++     |
| MongoDB |
| MySQL   |
| MongoDB |
| MongoDB |
| Java    |
| Java    |
+---------+
9 rows in set (0.00 sec)

如下是将SQL不同查询结果连接成一个字符串的查询语句 –

mysql> select group_concat(tbl.sub) from (select Subject sub from DemoTable group by Subject ) tbl;

输出

这将产生以下输出 –

+--------------------------+
| group_concat(tbl.sub)    |
+--------------------------+
| C,C++,MongoDB,MySQL,Java |
+--------------------------+
1 row in set (0.04 sec)