编辑代码

-- DQL 查询语言是运营用到最多的操作，关键操作词 select，查询的条件很多；网页的查询
-- 语法 select 字段 from 表名 where / group by /having /order by /limit ; 不了解 一个个来
-- 操作1 基本查询 
create database info;
use info;
create table worker(
    id int,
    name varchar(10),
    age int,
    sex char(1),
    city varchar(10),
    workertime date
);
-- show tables;
-- Desc worker;
insert into worker values (1,'张三',28,'F','上海','2020-08-20');
insert into worker values(2,'李四',24,'F','上海','2021-06-24');
insert into worker values(3,'王二麻',27,'M','北京','2020-07-22');
insert into worker values(4,'王五',29,'M','深圳','2022-01-10');
insert into worker values(5,'赵六',32,'F','深圳','2019-07-07');
insert into worker values(6,'钱九',31,'M','北京','2018-04-19');
insert into worker values(7,'孙八',30,'F','深圳','2021-09-17');
insert into worker values(8,'何十',34,'M','北京','2022-03-28');
insert into worker values(9,'九九',26,'M','深圳','2023-08-19');
insert into worker values(10,'零七',24,'F','上海','2021-06-24');
insert into worker values(11,'可可',27,'M','深圳','2024-07-21');
-- select * from worker;
-- 操作1 查询指定字段 并返回,语法是 select 字段1,字段2, from 表名;
-- select name,workertime,age from worker;
-- 操作2 查询整张表格 select * from 或者 select 字段1,字段2...所有字段 from 表名;
-- select * from worker;
-- select id,name,sex,city,workertime from worker;
-- 操作3 查询表中的某个字段，同时赋予字段别名，语法是 select 字段名 as 别名 from 表名；(as可以省略)
-- select city as '城市' from worker;
-- select city '城市' from worker;
-- 操作4 对查询出来的数据进行去重 distinct,语法是 select distinct 字段名（as 别名） from 表名
select distinct city '城市' from worker;
select distinct sex '性别' from worker;