CONCAT函数用于将两个字符串连接为一个字符串,试一下下面这个例子:
SELECT CONCAT("FIRST ", "SECOND"); +----------------------------+ | CONCAT("FIRST ", "SECOND") | +----------------------------+ | FIRST SECOND | +----------------------------+
要对 CONCAT函数有更为深入的了解,请考虑 employee_tbl表,表中记录如下所示:
(资料图)
SELECT * FROM employee_tbl; +------+------+------------+--------------------+ | id | name | work_date | daily_typing_pages | +------+------+------------+--------------------+ | 1 | John | 2022-08-24 | 250 | | 2 | Ramr | 2022-08-27 | 220 | | 3 | Jack | 2022-08-06 | 170 | | 3 | Jack | 2022-08-06 | 100 | | 4 | Jill | 2022-08-06 | 220 | | 5 | Zara | 2022-08-06 | 300 | | 5 | Zara | 2022-08-06 | 350 | +------+------+------------+--------------------+
现在,假设你想要将上表中所有的姓名(name)、id和工作日(work_date)连接在一起,那么可以通过如下的命令来达到目的:
SELECT CONCAT(id, name, work_date) FROM employee_tbl; +-----------------------------+ | CONCAT(id, name, work_date) | +-----------------------------+ | 1John2022-08-24 | | 2Ramr2022-08-27 | | 3Jack2022-08-06 | | 3Jack2022-08-06 | | 4Jill2022-08-06 | | 5Zara2022-08-06 | | 5Zara2022-08-06 | +-----------------------------+
还可以在字符中间添加符号
SELECT CONCAT(id,",",name,",",work_date) FROM employee_tbl; +-----------------------------+ | CONCAT(id, name, work_date) | +-----------------------------+ | 1,John,2022-08-24 | | 2,Ramr,2022-08-27 | | 3,Jack,2022-08-06 | | 3,Jack,2022-08-06 | | 4,Jill,2022-08-06 | | 5,Zara,2022-08-06 | | 5,Zara,2022-08-06 | +-----------------------------+ SELECT CONCAT(id,",",name,",",work_date) FROM employee_tbl; +-----------------------------+ | CONCAT(id, name, work_date) | +-----------------------------+ | 1,John,2022-08-24 | | 2,Ramr,2022-08-27 | | 3,Jack,2022-08-06 | | 3,Jack,2022-08-06 | | 4,Jill,2022-08-06 | | 5,Zara,2022-08-06 | | 5,Zara,2022-08-06 | +-----------------------------+
CONCAT_WS() 代表 CONCAT With Separator ,是CONCAT()的 特殊形式。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。
SELECT CONCAT(",",id,name,work_date) FROM employee_tbl; +-----------------------------+ | CONCAT(id, name, work_date) | +-----------------------------+ | 1,John,2022-08-24 | | 2,Ramr,2022-08-27 | | 3,Jack,2022-08-06 | | 3,Jack,2022-08-06 | | 4,Jill,2022-08-06 | | 5,Zara,2022-08-06 | | 5,Zara,2022-08-06 | +-----------------------------+
我们可以使用group_concat()函数将一整列打印到一行中,并且可以指定分隔的符号,默认为
,
SELECT GROUP_CONCAT(id) AS ids FROM employee_tbl +------------------+ | GROUP_CONCAT(id) | +------------------+ | 1,2,3,3,4,5,5 | +------------------+
将分隔符改为;
select group_concat(id separator ";") from employee_tbl; +------------------+ | GROUP_CONCAT(id) | +------------------+ | 1;2;3;3;4;5;5 | +------------------+
功能介绍:将多个字符串进行拼接。
语法:concat(字段,字段,字段,…)
concat实践
select CONCAT(id,",",age,",",name) AS line_info from user
如果连接串中存在NULL,则返回结果为NULL(我没遇到过):
select CONCAT(id,",",age,",",null) AS line_info from user
Null解决方案:
加一个 IFNULL()函数。
select CONCAT(id,",",age,",",IFNULL(name,"")) AS line_info from user
concat_ws
功能介绍:字符串拼接无需手动添加分隔符(自己理解)。
语法:concat_ws(分隔符,字段,字段,…)
concat_ws实践
select CONCAT_WS(",",id,age,name) AS line_info from user
select CONCAT_WS(",",concat(name),concat("年龄",age,"岁")) AS line_info from user
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