mysql 实现字符串的拼接

电玩女神 2022-04-23 03:12 311阅读 0赞

在Mysql 数据库中存在**两种字符串连接操作**.具体操作如下

一. 语法:

1. **CONCAT(string1,string2,…) **  说明 : string1,string2代表字符串,concat函数在连接字符串的时候，只要其中一个是NULL,那么将返回NULL

例1:

![20190123145753100.png][]

例2:

![20190123145753100.png][]

2. **CONCAT\_WS(separator,str1,str2,...)**

说明 : string1,string2代表字符串,**concat\_ws 代表 concat with separator,第一个参数是其它参数的分隔符**。分隔符的位置放在要连接的两个字符串之间。分隔符可以是一个字符串，也可以是其它参数。如果分隔符为 NULL，则结果为 NULL。函数会忽略任何分隔符参数后的 NULL 值。

举例1:

mysql> select concat\_ws('\#','courseName=','NX',null) AS nx\_courseName;  
\+-----------------------+  
| nx\_courseName |  
\+-----------------------+  
| courseName=\#NX|  
\+-----------------------+  
1 row in set (0.00 sec)

例2:

mysql> select concat\_ws('null','courseName=','NX',null) AS nx\_courseName;+-----------------------+  
| nx\_courseName |  
\+-----------------------+  
| NULL |  
\+-----------------------+  
1 row in set (0.00 sec)

**3. MySQL中group\_concat函数**  
完整的语法如下：  
group\_concat(\[DISTINCT\] 要连接的字段 \[Order BY ASC/DESC 排序字段\] \[Separator '分隔符'\])

基本查询

mysql> select \* from stu1;  
\+------+------+  
| id| name |  
\+------+------+  
|1 | 10|  
|1 | 20|  
|1 | 20|  
|2 | 20|  
|3 | 200   |  
|3 | 500   |  
\+------+------+  
6 rows in set (0.00 sec)

以id分组，把name字段的值打印在一行，逗号分隔(默认)

mysql> select id,**group\_concat(name)** from aa group by id;  
\+------+--------------------+  
| id| group\_concat(name) |  
\+------+--------------------+  
|1 | 10,20,20|  
|2 | 20 |  
|3 | 200,500|  
\+------+--------------------+  
3 rows in set (0.00 sec)

以id分组，把name字段的值打印在一行，分号分隔

mysql> select id,group\_concat(name separator ';') from aa group by id;  
\+------+----------------------------------+  
| id| group\_concat(name separator ';') |  
\+------+----------------------------------+  
|1 | 10;20;20 |  
|2 | 20|  
|3 | 200;500   |  
\+------+----------------------------------+  
3 rows in set (0.00 sec)

以id分组，把去冗余的name字段的值打印在一行，

逗号分隔

mysql> select id,group\_concat(distinct name) from aa group by id;  
\+------+-----------------------------+  
| id| group\_concat(distinct name) |  
\+------+-----------------------------+  
|1 | 10,20|  
|2 | 20   |  
|3 | 200,500 |  
\+------+-----------------------------+  
3 rows in set (0.00 sec)

以id分组，把name字段的值打印在一行，逗号分隔，以name排倒序

mysql> select id,group\_concat(name order by name desc) from aa group by id;  
\+------+---------------------------------------+  
| id| group\_concat(name order by name desc) |  
\+------+---------------------------------------+  
|1 | 20,20,10   |  
|2 | 20|  
|3 | 500,200|  
\+------+---------------------------------------+  
3 rows in set (0.00 sec)

***还有一个简单的连接方式为: ||***

mysql> select \*  from student;  
\+----+------+-------+----------+------------+  
| id | age  | score | name     | birth      |  
\+----+------+-------+----------+------------+  
|  1 |   23 |    78 | 李四     | 2017-10-10 |  
|  2 |   24 |    78 | zhangsan | 2017-10-10 |  
|  3 |   25 |    99 | 王五     | 2016-05-17 |  
\+----+------+-------+----------+------------+  
3 rows in set (0.00 sec)  
  
mysql> select id+999,name,name+99,name+'999' from student;  
\+--------+----------+---------+------------+  
| id+999 | name     | name+99 | name+'999' |  
\+--------+----------+---------+------------+  
|   1000 | 李四     |      99 |        999 |  
|   1001 | zhangsan |      99 |        999 |  
|   1002 | 王五     |      99 |        999 |  
\+--------+----------+---------+------------+  
3 rows in set, 6 warnings (0.00 sec)

[20190123145753100.png]: /images/20220323/61cb3776a55240a38276df744e849b5a.png