基本的SELECT语句
• 过滤和排序数据
• 分组函数
• 分组查询
• 多表查询
• 分页查询
（1）SELECT
SELECT *|{[DISTINCT] column|expression [alias],...} FROM table
示例：select * from student where name = ‘lin min’
选择所有列： SELECT * FROM departments;
选择特定的列：SELECT department_id, location_id FROM departments;
使用别名：SELECT last_name AS name, commission_pct comm FROM employees;
显示表结构：desc table_name
过滤和排序数据: SELECT *|{[DISTINCT] column|expression [alias],...} FROM table [WHERE condition(s)];
Select * from employees where 操作符 = ‘’ //
操作符： =，>，>=，<，<=，<>，BETWEEN...AND...，IN(set)
，LIKE，IS NULL，AND，OR，NOT
ORDER BY 子句：使用 ORDER BY 子句排序
– ASC（ascend）: 升序
– DESC（ descend ）: 降序
• ORDER BY 子句在SELECT 语句的 结尾
降序排序：S
SELECT last_name, job_id, department_id, hire_date
FROM employees ORDER BY hire_date DESC ;
（2）组函数
组函数类型：
• AVG()
• COUNT()
• MAX()
• MIN()
• SUM()
（3）分组
GROUP BY 子句语法
SELECT department_id, AVG(salary) FROM employees GROUP BY department_id ;
SELECT job_id,MAX(salary) FROM employees GROUP BY job_id
非法使用组函数：不能在 WHERE 子句中使用组函数。
（4）HAVING 子句
SELECT department_id, MAX(salary) FROM employees GROUP BY department_id HAVING MAX(salary)>10000 ;
（5） 多表查询
select name,boyName from beauty,boys; 两个表之间可以用,隔开
SELECT * FROM departments,employees 本质就是求两个表的交集
SELECT table1.column, table2.column
FROM table1, table2
WHERE table1.column1 = table2.column2;
Join连接：
内连接 [inner] join on
– 外连接
左外连接 left [outer] join on
右外连接 right [outer] join on