mysql 数据库 IV（单表查询）
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1.今日内容
单表查询语法
select distinct 字段1，字段2... from 表名 where 条件 group by 字段 having 筛选 order by 字段 limit 限制条数关键字执行的优先级
from # 找到表 where # 拿着where指定的约束条件，去文件/表中取出一条条记录 group by # 将取出来的数据进行group by，如果没有group by，则整体做为一组 select distinct #执行select-去重 having #将分组的结果进行having过滤 order by #将结果按条件排序，order by limit #限制结果的显示条数
2.具体内容
简单查询
建表准备工作
mysql #创建表 mysql> create table employee( -> id int not null unique auto_increment, -> emp_name varchar(20) not null, -> sex enum('male','female') not null default 'female', -> 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, -> depart_id int -> ); Query OK, 0 rows affected (0.04 sec) #查看表结构 mysql> desc employee; +--------------+-----------------------+------+-----+---------+--- -------------+ | Field | Type | Null | Key | Default | Extra | +--------------+-----------------------+------+-----+---------+--- -------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | emp_name | varchar(20) | NO | | NULL | | | sex | enum('male','female') | NO | | female | | | age | int(3) unsigned | NO | | 28 | | | hire_date | date | NO | | NULL | | | post | varchar(50) | YES | | NULL | | | post_comment | varchar(100) | YES | | NULL | | | salary | double(15,2) | YES | | NULL | | | office | int(11) | YES | | NULL | | | depart_id | int(11) | YES | | NULL | | +--------------+-----------------------+------+-----+---------+--- -------------+ 10 rows in set (0.02 sec) #插入数据 mysql> insert into employee(emp_name,sex,age,hire_date,post,salary,office,depart_id) values -> ('egon','male',18,'20170301','老男孩驻沙河办事处外交大 使',7300.33,401,1), -> ('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), -> ('成龙','male',48,'20101111','teacher',10000,401,1), -> ('歪歪','female',48,'20150311','sale',3000.13,402,2), -> ('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), -> ('张野','male',28,'20160311','operation',10000.13,403,3), -> ('程咬金','male',18,'19970312','operation',20000,403,3), -> ('程咬银','female',18,'20130311','operation',19000,403,3), -> ('程咬铜','male',18,'20150411','operation',18000,403,3), -> ('程咬铁','female',18,'20140512','operation',17000,403,3) -> ; Query OK, 18 rows affected (0.01 sec) Records: 18 Duplicates: 0 Warnings: 0 mysql> select * from employee; +----+------------+--------+-----+------------+------------------- ----------------------+--------------+------------+--------+------ -----+ | id | emp_name | sex | age | hire_date | post | post_comment | salary | office | depart_id | +----+------------+--------+-----+------------+------------------- ----------------------+--------------+------------+--------+------ -----+ | 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外 交大使 | NULL | 7300.33 | 401 | 1 | | 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 | | 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 | | 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 | | 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 | | 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 | | 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 | | 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 | | 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 | | 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 | | 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 | | 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 | | 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 | | 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 | | 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 | | 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 | | 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 | | 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 | +----+------------+--------+-----+------------+------------------- ----------------------+--------------+------------+--------+------ -----+ 18 rows in set (0.00 sec)
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