作用:

　　解決一開始數據庫建立不合理造成的字段冗余，從而提取部分字段，數據遷移、拼接字符串的功能。

格式：

　　concat(字段1,‘間隔符‘,字段2....)

　　concat_ws(‘間隔符‘,字段1，字段2)

數據準備：

#創建表
create table employee(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum(‘male‘,‘female‘) not null default ‘male‘, #大部分是男的
age int(3) unsigned not null default 28,
hire_date date 
 
not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一個部門一個屋子
depart_id int
);
#插入記錄
#三個部門：教學，銷售，運營
insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
(‘egon‘,‘male‘,18,‘20170301‘,‘老男孩駐沙河辦事處外交大使‘,7300.33,401,1), #以下是教學部
(‘alex‘,‘male‘,78,‘20150302
 
‘,‘teacher‘,1000000.31,401,1),
(‘wupeiqi‘,‘male‘,81,‘20130305‘,‘teacher‘,8300,401,1),
(‘yuanhao‘,‘male‘,73,‘20140701‘,‘teacher‘,3500,401,1),
(‘liwenzhou‘,‘male‘,28,‘20121101‘,‘teacher‘,2100,401,1),
(‘jingliyang‘,‘female‘,18,‘20110211‘,‘teacher‘,9000,401,1),
(‘jinxin‘,‘male‘,18,‘19000301‘,‘teacher‘,30000,401,1),
(‘成龍‘,‘male‘,48,‘20101111‘,‘
 
teacher‘,10000,401,1),

(‘歪歪‘,‘female‘,48,‘20150311‘,‘sale‘,3000.13,402,2),#以下是銷售部門
(‘丫丫‘,‘female‘,38,‘20101101‘,‘sale‘,2000.35,402,2),
(‘丁丁‘,‘female‘,18,‘20110312‘,‘sale‘,1000.37,402,2),
(‘星星‘,‘female‘,18,‘20160513‘,‘sale‘,3000.29,402,2),
(‘格格‘,‘female‘,28,‘20170127‘,‘sale‘,4000.33,402,2),

(‘張野‘,‘male‘,28,‘20160311‘,‘operation‘,10000.13,403,3), #以下是運營部門
(‘程咬金‘,‘male‘,18,‘19970312‘,‘operation‘,20000,403,3),
(‘程咬銀‘,‘female‘,18,‘20130311‘,‘operation‘,19000,403,3),
(‘程咬銅‘,‘male‘,18,‘20150411‘,‘operation‘,18000,403,3),
(‘程咬鐵‘,‘female‘,18,‘20140512‘,‘operation‘,17000,403,3)
;

　　操作示例：

　　只做字符串的拼接：

 1 mysql> select concat(‘name:‘,name) as mingzi,concat(‘sex:‘,sex) from  emp;
 2 +-----------------+--------------------+
 3 | mingzi          | concat(‘sex:‘,sex) |
 4 +-----------------+--------------------+
 5 | name:egon       | sex:male           |
 6 | name:alex       | sex:male           |
 7 | name:wupeiqi    | sex:male           |
 8 | name:yuanhao    | sex:male           |
 9 | name:liwenzhou  | sex:male           |
10 | name:jingliyang | sex:female         |
11 | name:jinxin     | sex:male           |
12 | name:成龍       | sex:male           |
13 | name:歪歪       | sex:female         |
14 | name:丫丫       | sex:female         |
15 | name:丁丁       | sex:female         |
16 | name:星星       | sex:female         |
17 | name:格格       | sex:female         |
18 | name:張野       | sex:male           |
19 | name:程咬金     | sex:male           |
20 | name:程咬銀     | sex:female         |
21 | name:程咬銅     | sex:male           |
22 | name:程咬鐵     | sex:female         |
23 +-----------------+--------------------+
24 18 rows in set (0.00 sec)

　　數據遷移（同時進行字符串拼接）：

 1 mysql> create table aa select concat(‘name:‘,name) as mingzi,concat(‘sex:‘,sex) from  emp;
 2 Query OK, 18 rows affected (0.03 sec)
 3 Records: 18  Duplicates: 0  Warnings: 0
 4 
 5 mysql>
 6 mysql> show tables;
 7 +---------------+
 8 | Tables_in_db2 |
 9 +---------------+
10 | aa            |
11 | big_data      |
12 | emp           |
13 +---------------+
14 3 rows in set (0.00 sec)
15 
16 mysql> select * from aa ;
17 +-----------------+--------------------+
18 | mingzi          | concat(‘sex:‘,sex) |
19 +-----------------+--------------------+
20 | name:egon       | sex:male           |
21 | name:alex       | sex:male           |
22 | name:wupeiqi    | sex:male           |
23 | name:yuanhao    | sex:male           |
24 | name:liwenzhou  | sex:male           |
25 | name:jingliyang | sex:female         |
26 | name:jinxin     | sex:male           |
27 | name:成龍       | sex:male           |
28 | name:歪歪       | sex:female         |
29 | name:丫丫       | sex:female         |
30 | name:丁丁       | sex:female         |
31 | name:星星       | sex:female         |
32 | name:格格       | sex:female         |
33 | name:張野       | sex:male           |
34 | name:程咬金     | sex:male           |
35 | name:程咬銀     | sex:female         |
36 | name:程咬銅     | sex:male           |
37 | name:程咬鐵     | sex:female         |
38 +-----------------+--------------------+
39 18 rows in set (0.00 sec)

使用concat做字符串拼接和數據遷移