简单查询：select * from '表名';

避免重复：select distinct '字段' from '表名';

条件查询：select 字段,字段 from 表名 where id<=5(条件);

四则运算查询：select id,dep_id,id*dep_id from company.employee5 where id<=5;

定义显示格式一：select id*dep_id as "id and dep_id's sum" from company.employee5 where id<=5;

定义显示格式：SELECT CONCAT(name, ' annual salary: ', salary*14) AS Annual_salary FROM employee5;   //定义格式+四个运算，CONCAT是关键字

多条件：select '字段，字段‘ from '表名' WHERRE '条件一' AND '条件二';

关键字between and：

select '字段，字段' from '表名' where 字段 BETWEEN

'条件一' AND '条件二';

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排序查询：

select '字段' from '表名' ORDER BY '排序字段'；//字段后加DESC正序，ASC反序

限制查询的记录数：

select '字段' from '表名' ORDER BY '字段，DESC|ACS' LIMIT '数字'; //数字有两种的是(5,从初始位置到第五个)(2,5,第三个开始，共显示五个)

使用集合的查询：

select COUNT(*) from '表名'；

select COUNT(*) FROM '表名' WHERE dep_id=101;

select MAX(salary) FROM '表名';

select MIN(salary) FROM '表名';

select AVG(salary) FROM '表名';

select SUM(salary) FROM '表名';

select SUM(salary) FROM '表名' WHERE dep_id=101;

分组查询：

select '字段' from '表名' group by 字段;   //可参考下列面试题

模糊查询：

select '字段' from '表名' LIKE '关键字'；

正则表达式查询：

select * from '表名' where '字段' REGEXP '关键字'；