目錄

• MySQL函數(shù)CONCAT、CONCAT_WS、GROUP_CONCAT
• 1.concat()函數(shù)
• 2.concat_ws()函數(shù)
• 3.group_concat()函數(shù)
• 補(bǔ)充：Mysql concat_ws、concat函數(shù)使用
• 一、概念 concat
• 二、混合使用函數(shù)實(shí)戰(zhàn)

MySQL函數(shù)CONCAT、CONCAT_WS、GROUP_CONCAT

1.concat()函數(shù)

CONCAT 函數(shù)用于將兩個(gè)字符串連接為一個(gè)字符串，試一下下面這個(gè)例子：

	SELECT CONCAT("FIRST ", "SECOND");    +----------------------------+    | CONCAT("FIRST ", "SECOND") |    +----------------------------+    | FIRST SECOND       |    +----------------------------+

要對(duì) CONCAT 函數(shù)有更為深入的了解，請(qǐng)考慮 employee_tbl 表，表中記錄如下所示：

    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 |    +------+------+------------+--------------------+

現(xiàn)在，假設(shè)你想要將上表中所有的姓名（name）、id和工作日（work_date）連接在一起，那么可以通過如下的命令來(lái)達(dá)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     |    +-----------------------------+

還可以在字符中間添加符號(hào)

 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   |    +-----------------------------+

2.concat_ws()函數(shù)

CONCAT_WS() 代表 CONCAT With Separator ，是CONCAT()的 特殊形式。第一個(gè)參數(shù)是其它參數(shù)的分隔符。分隔符的位置放在要連接的兩個(gè)字符串之間。分隔符可以是 一個(gè)字符串，也可以是其它參數(shù)。

 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   |    +-----------------------------+

3.group_concat()函數(shù)

我們可以使用group_concat()函數(shù)將一整列打印到一行中，并且可以指定分隔的符號(hào)，默認(rèn)為,

	SELECT GROUP_CONCAT(id) AS ids FROM employee_tbl    +------------------+    | GROUP_CONCAT(id) |    +------------------+    | 1,2,3,3,4,5,5    |    +------------------+

將分隔符改為；

  	select group_concat(id separator ";") from employee_tbl;    +------------------+    | GROUP_CONCAT(id) |    +------------------+    | 1;2;3;3;4;5;5    |    +------------------+

補(bǔ)充：Mysql concat_ws、concat函數(shù)使用

一、概念 concat

功能介紹： 將多個(gè)字符串進(jìn)行拼接。
語(yǔ)法： concat(字段,字段,字段,…)

concat實(shí)踐

select CONCAT(id,",",age,",",name) AS line_info from user

如果連接串中存在NULL，則返回結(jié)果為NULL（我沒遇到過）：

select CONCAT(id,",",age,",",null) AS line_info from user

Null解決方案：

加一個(gè) IFNULL()函數(shù)。

select CONCAT(id,",",age,",",IFNULL(name,"")) AS line_info from user

concat_ws

功能介紹： 字符串拼接無(wú)需手動(dòng)添加分隔符（自己理解）。
語(yǔ)法：concat_ws(分隔符,字段,字段,…)

concat_ws實(shí)踐

select CONCAT_WS(",",id,age,name) AS line_info from user

二、混合使用函數(shù)實(shí)戰(zhàn)

select CONCAT_WS(",",concat(name),concat("年齡",age,"歲")) AS line_info from user

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