INSERT

基本语法：INSERT INTO table_name VALUES(value1,value2,value3,...); 

指定列：INSERT INTO table_name(column1, column2, column3,…) VALUES(value1,value2,value3,...);

UPDATE

UPDATE table_name set column1=‘new_value‘,column2=‘new_value‘,...;

DELETE

DELETE from table_name;

SELECT

SELECT column1,column2,column3,... from table_name; or

SELECT *  from table_name;

WHERE condition GROUP BY column1,column2,...HAVING condition

分组要有据（select columns 有该字段），先有结果集（可以是where帅选过的），再依据唯一性分组，然后统计，最后过滤结果集。

a sample Employees table

求各个部门的总工资：

SELECT DEPARTMENT_ID,SUM(SALARY) as Total_Salary FROM EmployeesGROUP BY DEPARTMENT_ID;

group by DEPARTMENT_ID后具有相同DEPARTMENT_ID的数据项聚集在一起，然后以函数的形式合并成一条记录，DEPARTMENT_ID具备了唯一性（group by后的字段组合具有唯一性）。

sql 语句