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SQL学习/DDL操作集合.sql

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+show DATABASES;
+
+drop database nengdie;
+
+create database nengdie;
+
+show CREATE DATABASE nengdie;
+
+use nengdie;
+
+# can not rename database
+# alter nengdie rename nengdie woshinibaba;
+
+# delete a table
+drop table user_info;
+
+# create a table
+create table user_info (
+   user_id TINYINT(3) PRIMARY KEY,
+   user_name VARCHAR(30) not null,
+   email_address VARCHAR(50),
+   age SMALLINT(4) not null,
+   gender VARCHAR(5) DEFAULT 'male'
+);
+
+# read all tables
+show tables;
+
+# read a table
+describe user_info;
+show create table user_info;
+
+# modify a table
+
+## change table name
+alter table user_info rename user_information;
+show tables;
+alter table nengdie.user_information rename user_info;
+show tables;
+
+## add a column
+alter table user_info add column favoriteID tinyint after age;
+describe user_info;
+
+## change column position
+alter table user_info modify favoriteID smallint after gender;
+
+## change column name
+alter table user_info change favoriteID fav_id tinyint;
+
+## modify column data format
+alter table user_info modify gender varchar(10);
+
+## delete a column
+alter table user_info drop fav_id;
+alter table user_info add fav_id tinyint after age;
+
+## modify column CONSTRAINTS
+alter table user_info modify user_id tinyint auto_increment;
+
+# DML insert records into a table user_info
+insert into user_info( nengdie.user_info.user_name, nengdie.user_info.email, nengdie.user_info.age, nengdie.user_info.gender)
+values
+       ('wangdada','zeaslity@qq.com',15,'male'),
+       ('cxc','cxc@163.com',12,'male'),
+       ('nengdie','nengdie@qq.com',30,'male'),
+       ('hong','hong@qq.com',25,'female'),
+       ('zeaslity','zeaslity@qq.com',18,'male'),
+       ('zey','zety@qq.com',18,'male'),
+       ('die','die@qq.com',15,'male');
+
+SELECT * FROM user_info;
+
+describe user_info;
+describe fav_thing;
+
+## 内连接，只输出符合限定条件的内容
+select user_name,age,gender from user_info
+inner join
+    fav_thing as t on user_id = t.fav_user_id
+order by age;
+
+## left outer join 左外连接  讲用户的喜好表 fav_thing与user表连接，查看用户对应喜好的事情
+select * from  user_info
+left join
+    fav_thing as t on user_id =t.fav_user_id
+order by age;
+
+## 全外连接
+select *
+from user_info
+full join fav_thing;
+
+# 交叉连接
+select * from user_info
+cross join fav_thing;