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详解MySQL拼接函数CONCAT的使用心得

_陈哈哈 人气:0

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)

在这里插入图片描述

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,…)

  CONCAT_WS() 函数全称: CONCAT With Separator ,是CONCAT()的特殊形式。第一个参数(separator)是其它参数的分隔符。分隔符的位置在要连接的两个字符串之间。分隔符可以是一个字符串,也可以是其它字段参数。

需要注意的是:

  如果分隔符为 NULL,则结果为 NULL;但如果分隔符后面的参数为NULL,只会被直接忽略掉,而不会导致结果为NULL。

好了,我们依旧用上面的LOL表,连接各字段,以逗号分隔:

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'] )

  group_concat函数通常用于有group by的查询语句,group_concat一般包含在查询返回结果字段中。

  是不是group_concat函数的公式看着还挺复杂的?我们一起看看,上方公式中 [] 括号是可选项,表示可用可不用;

  好了,下面让我们来进入开心的测试环节吧~ 还是用这张LOL表,别问为什么。或许这就是青春吧!还记的那年通宵五排,大龙团的时候网吧停电了…

在这里插入图片描述

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)

  举个场景,我们要区分出各个价格段的英雄来,如果不用group_concat的话,或许只能用order by区分了。

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)

  那么GROUP_CONCAT函数中的order by 排序怎么用?是用在了拼接字段的排序上,如根据hero_title进行排序拼接,如下:

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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