MySQL通过DQL实现对数据库数据的基本查询

目录

• SQL
• DQL
• DQL查询类型分类
• DQL-基本查询
• 1.查询多个字段
• 2.设置别名
• 3.去除重复记录

SELECT
    字段列表
FROM
    表名列表
WHERE
    条件列表
GROUP BY
    分组字段列表
HAVING
    分组后条件列表
ORDER BY 
    排序字段列表
LIMIT 
    分页参数

CREATE TABLE emp
(

ID INT COMMENT '编号',

WORKNO VARCHAR(10) COMMENT '工号',

NAME VARCHAR(10) COMMENT '姓名',

GENDER CHAR(1) COMMENT '性别',

AGE TINYINT UNSIGNED COMMENT '年龄',

IDCARD CHAR(18) COMMENT '身份证号',

WORKADDRESS VARCHAR(50) COMMENT '工作地址',

ENTRYDATE DATE COMMENT '入职时间'

) COMMENT '员工表';

INSERT INTO emp (ID, WORKNO, NAME, GENDER, AGE, IDCARD, WORKADDRESS, ENTRYDATE)

VALUES (null, '1', '柳岩', '女', 20, '123456789012345678', '北京', '2000-01-01'),

(null, '2', '张无忌', '男', 18, '123456789012345670', '北京', '2005-09-01'),

(null, '3', '韦一笑', '男', 38, '123456789012345670', '上海', '2005-08-01'),

(null, '4', '赵敏', '女', 18, '123456789012345670', '北京', '2009-12-01'),

(null, '5', '小昭', '女', 16, '123456789012345678', '上海', '2007-07-01'),

(null, '6', '杨逍', '男', 28, '12345678901234567X', '北京', '2006-01-01'),

(null, '7', '范瑶', '男', 40, '123456789012345670', '北京', '2005-05-01'),

(null, '8', '黛绮丝', '女', 38, '123456789012345670', '天津', '2015-05-01'),

(null, '9', '范凉凉', '女', 45, '123456789012345678', '北京', '2010-04-01'),

(null, '10', '陈友谅', '男', 53, '123456789012345670', '上海', '2011-01-01'),

(null, '11', '张士诚', '男', 55, '123456789012345670', '江苏', '2015-05-01'),

(null, '12', '常遇春', '男', 32, '123456789012345670', '北京', '2004-02-01'),

(null, '13', '张三丰', '男', 88, '123456789012345678', '江苏', '2020-11-01'),

(null, '14', '灭绝', '女', 65, '123456789012345670', '西安', '2019-05-01'),

(null, '15', '胡青牛', '男', 70, '12345678901234567X', '西安', '2018-04-01'),

(null, '16', '周芷若', '女', 18, NULL, '北京', '2012-06-01');

select name, WORKNO,AGE from emp;

select * from emp;

select WORKADDRESS from emp;

select WORKADDRESS as '工作地址' from emp;

select distinct WORKADDRESS as '工作地址' from emp;