基本的SELECT语句

Posted 2022-12-03 嫚嫚_

-- source d:\\mysqldb.sql
SELECT * FROM employees;
-- 列的别名
 SELECT first_name emp_id,last_name AS lname ,department_id "部门id"FROM employees;

-- 7: 去除重复行
SELECT DISTINCT department_id,salary FROM employees;


-- 8:空值参与运算
-- NULL !=0
SELECT employee_id ,salary "月工资",salary*(1+commission_pct)*12 "年工资",commission_pct
FROM employees;
-- 实际问题解决方案

SELECT employee_id ,salary "月工资",salary*(1+IFNULL (commission_pct,0))*12 "年工资",commission_pct
FROM employees;


-- 9:着重号``
SELECT * FROM `order`;

-- 10:查询常数
SELECT '尚硅谷',123,employee_id FROM employees;

-- 11：显示表结构
DESCRIBE employees;# 显示表中的详细信息
DESC jobs;
-- 12:过滤数据
SELECT *FROM employees
-- 过滤条件
WHERE last_name='king';

-- 练习1 
# 1.查询员工12个月的工资总和，并起别名为ANNUAL SALARY
SELECT DISTINCT job_id FROM employees;