详解MySQL拼接函数CONCAT的使用心得

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前几篇文章给大家介绍了MySQL中的替换函数（Replace）、切分函数（SubString），今天我们一起来看看MySQL专业拼接“字符串”的函数：concat。老规矩，有好的建议和想法，记得写到评论中，等我上班摸鱼时，跟大家一起吃瓜~

一、concat函数相关的几种用法

1-1、函数：concat(str1,str2,…)

concat 函数一般用在SELECT 查询语法中，用于修改返回字段内容，例如有张LOL英雄信息表如下

mysql> select * from `LOL`;
+----+---------------+--------------+-------+
| id | hero_title  | hero_name  | price |
+----+---------------+--------------+-------+
| 1 | D刀锋之影   | 泰隆     | 6300 |
| 2 | X迅捷斥候   | 提莫     | 6300 |
| 3 | G光辉女郎   | 拉克丝    | 1350 |
| 4 | F发条魔灵   | 奥莉安娜   | 6300 |
| 5 | Z至高之拳   | 李青     | 6300 |
| 6 | W无极剑圣   | 易      |  450 |
| 7 | J疾风剑豪   | 亚索     |  450 |
+----+---------------+--------------+-------+
7 rows in set (0.00 sec)

我需要返回一列：英雄称号 - 英雄名称的数据，这是就用到了concat函数，如下：

SELECT CONCAT(hero_title,' - ',hero_name) as full_name, price from `LOL`;

mysql> SELECT CONCAT(hero_title,' - ',hero_name) as full_name, price from `LOL`;
+------------------------------+-------+
| full_name          | price |
+------------------------------+-------+
| D刀锋之影 - 泰隆       | 6300 |
| X迅捷斥候 - 提莫       | 6300 |
| G光辉女郎 - 拉克丝      | 1350 |
| F发条魔灵 - 奥莉安娜     | 6300 |
| Z至高之拳 - 李青       | 6300 |
| W无极剑圣 - 易        |  450 |
| J疾风剑豪 - 亚索       |  450 |
+------------------------------+-------+
7 rows in set (0.00 sec)

如果拼接的参数中有NULL，则返回NULL；如下：

SELECT CONCAT(hero_title,NULL,hero_name) as full_name, price from `LOL`;

mysql> SELECT CONCAT(hero_title,'NULL',hero_name) as full_name, price from `LOL`;
+-------------------------------+-------+
| full_name           | price |
+-------------------------------+-------+
| D刀锋之影NULL泰隆       | 6300 |
| X迅捷斥候NULL提莫       | 6300 |
| G光辉女郎NULL拉克丝      | 1350 |
| F发条魔灵NULL奥莉安娜     | 6300 |
| Z至高之拳NULL李青       | 6300 |
| W无极剑圣NULL易        |  450 |
| J疾风剑豪NULL亚索       |  450 |
+-------------------------------+-------+
7 rows in set (0.00 sec)

不好意思，上面是我弟弟写的，正确的如下：

mysql> SELECT CONCAT(hero_title,NULL,hero_name) as full_name, price from `LOL`;
+-----------+-------+
| full_name | price |
+-----------+-------+
| NULL   | 6300 |
| NULL   | 6300 |
| NULL   | 1350 |
| NULL   | 6300 |
| NULL   | 6300 |
| NULL   |  450 |
| NULL   |  450 |
+-----------+-------+
7 rows in set (0.00 sec)

1-2、函数：concat_ws(separator,str1,str2,…)

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select concat_ws(',',hero_title,hero_name,price) as full_name, price from `LOL`;

mysql> select concat_ws(',',hero_title,hero_name,price) as full_name, price from `LOL`;
+---------------------------------+-------+
| full_name            | price |
+---------------------------------+-------+
| D刀锋之影,泰隆,6300       | 6300 |
| X迅捷斥候,提莫,6300       | 6300 |
| G光辉女郎,拉克丝,1350      | 1350 |
| F发条魔灵,奥莉安娜,6300     | 6300 |
| Z至高之拳,李青,6300       | 6300 |
| W无极剑圣,易,450        |  450 |
| J疾风剑豪,亚索,450       |  450 |
+---------------------------------+-------+
7 rows in set (0.00 sec)

分隔符后的拼接参数为NULL时，直接忽略，不会影响整体结果，如下：

select concat_ws(',',hero_title,NULL,hero_name) as full_name, price from `LOL`;

mysql> select concat_ws(',',hero_title,NULL,hero_name) as full_name, price from `LOL`;
+----------------------------+-------+
| full_name         | price |
+----------------------------+-------+
| D刀锋之影,泰隆       | 6300 |
| X迅捷斥候,提莫       | 6300 |
| G光辉女郎,拉克丝      | 1350 |
| F发条魔灵,奥莉安娜     | 6300 |
| Z至高之拳,李青       | 6300 |
| W无极剑圣,易        |  450 |
| J疾风剑豪,亚索       |  450 |
+----------------------------+-------+
7 rows in set (0.00 sec)

分隔符为NULL时，结果返回NULL，如下：

select concat_ws(NULL,hero_title,hero_name,price) as full_name, price from `LOL`;

mysql> select concat_ws(NULL,hero_title,hero_name,price) as full_name, price from `LOL`;
+-----------+-------+
| full_name | price |
+-----------+-------+
| NULL   | 6300 |
| NULL   | 6300 |
| NULL   | 1350 |
| NULL   | 6300 |
| NULL   | 6300 |
| NULL   |  450 |
| NULL   |  450 |
+-----------+-------+
7 rows in set (0.00 sec)

1-3、函数：group_concat(expr)

group_concat ( [DISTINCT] 字段名 [order by 排序字段 ASC/DESC] [Separator ‘分隔符'] )

"text-align: center">

又跑题了。。不好意思。

mysql> select * from `LOL`;
+----+---------------+--------------+-------+
| id | hero_title  | hero_name  | price |
+----+---------------+--------------+-------+
| 1 | D刀锋之影   | 泰隆     | 6300 |
| 2 | X迅捷斥候   | 提莫     | 6300 |
| 3 | G光辉女郎   | 拉克丝    | 1350 |
| 4 | F发条魔灵   | 奥莉安娜   | 6300 |
| 5 | Z至高之拳   | 李青     | 6300 |
| 6 | W无极剑圣   | 易      |  450 |
| 7 | J疾风剑豪   | 亚索     |  450 |
+----+---------------+--------------+-------+
7 rows in set (0.00 sec)

"htmlcode">

select * from `LOL` order by price desc;

mysql> select * from `LOL` order by price desc;
+----+---------------+--------------+-------+
| id | hero_title  | hero_name  | price |
+----+---------------+--------------+-------+
| 1 | D刀锋之影   | 泰隆     | 6300 |
| 2 | X迅捷斥候   | 提莫     | 6300 |
| 4 | F发条魔灵   | 奥莉安娜   | 6300 |
| 5 | Z至高之拳   | 李青     | 6300 |
| 3 | G光辉女郎   | 拉克丝    | 1350 |
| 6 | W无极剑圣   | 易      |  450 |
| 7 | J疾风剑豪   | 亚索     |  450 |
+----+---------------+--------------+-------+
7 rows in set (0.00 sec)

但是这样很不直观啊，我想一行都看到，怎么办？

SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price 
 from `LOL` GROUP BY price ORDER BY price desc;

这时GROUP_CONCAT函数就轻松的帮你解决了这个问题。看，舒服不~

注释：这里我是拼接了（hero_title,' - ‘,hero_name）这三个参数，分隔符设为：','，根据价格来分组，根据价格来排的序。效果如下

mysql> SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price desc;
+------------------------------------------------------------------------+-------+
| full_name                               | price |
+------------------------------------------------------------------------+-------+
| D刀锋之影 - 泰隆,X迅捷斥候 - 提莫,F发条魔灵 - 奥莉安娜,Z至高之拳 - 李青     | 6300 |
| G光辉女郎 - 拉克丝                            | 1350 |
| W无极剑圣 - 易,J疾风剑豪 - 亚索                      |  450 |
+------------------------------------------------------------------------+-------+
3 rows in set (0.00 sec)

如果按价格（price）从小到大排序，只需控制外层ORDER BY即可，如下：

SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price 
  from `LOL` GROUP BY price ORDER BY price asc;

mysql> SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc;
+-------------------------------------------------------------------------+-------+
| full_name                                | price |
+-------------------------------------------------------------------------+-------+
| W无极剑圣 - 易,J疾风剑豪 - 亚索                      |  450 |
| G光辉女郎 - 拉克丝                            | 1350 |
| D刀锋之影 - 泰隆,X迅捷斥候 - 提莫,F发条魔灵 - 奥莉安娜,Z至高之拳 - 李青     | 6300 |
+-------------------------------------------------------------------------+-------+
3 rows in set (0.00 sec)

"htmlcode">

SELECT GROUP_CONCAT(hero_title,' - ',hero_name order by hero_title Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc;

mysql> SELECT GROUP_CONCAT(hero_title,' - ',hero_name order by hero_title Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc;
+-------------------------------------------------------------------------+-------+
| full_name                                | price |
+-------------------------------------------------------------------------+-------+
| J疾风剑豪 - 亚索,W无极剑圣 - 易                       |  450 |
| G光辉女郎 - 拉克丝                            | 1350 |
| D刀锋之影 - 泰隆,F发条魔灵 - 奥莉安娜,X迅捷斥候 - 提莫,Z至高之拳 - 李青     | 6300 |
+-------------------------------------------------------------------------+-------+
3 rows in set (0.00 sec)

好了，可以看出，MySQL中的concat拼接函数还是很好用的，希望你在有类似的需求或困惑时，想到它！或者能找到这篇博客，帮到你！

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