【MySQL】基本SQL語句

DDL:

庫

• 創建庫：create database dataname;
  eg. create database 軟工1601班;
• 刪除庫：drop database databasename;
  eg. drop database 軟工1601班;
• 查看所有庫：show databases;

表

• 創建表：create table tablename(字段名稱，字段類型，字段約束，
  字段名稱，字段類型，字段約束，…)
  eg. create table stu(
  name varchar(10)，not null COMMENT “姓名”，
  id varchar(10)，primary key，COMMENT “學號”，
  sex enum(“man”，“woman”) COMMENT “性別”
  age int COMMENT “年齡”
  );
• 刪除表：drop table tablename;
  eg.drop table stu;
• 修改表
  • 修改字段類型：modify
    eg.alter table stu modify name varchar(50);
  • 修改字段名稱：change
    eg.alter table stu change id sid varchar(20);
  • 添加字段：add [after first]
    eg.alter table stu add score float not null first;
  • 刪除字段：drop
    eg. alter table stu drop score;
  • 修改表名：rename
    eg.alter table stu rename student;
• 查看錶
  • 查看錶的創建
    show create table tablename;
  • 查看字段
    desc tablename;

字段約束

主鍵 primary key
外鍵 foreign key
唯一 unique
非空 not null
爲空 default null

字段類型

字段類型 date time datetime

DML:

插入:insert or load

• 插入數據：
  insert into
  tablename [(field1，field2，field3，…)]
  *values(data1，data2，…);
  • eg1.insert into stu values
    (“002”，“張三”，“woman”，19)，
    (“003”，“李四”，“man”，20);
  • eg2.insert into
    stu(id,name)
    values(“004”,“王五”);

刪除:delete

刪除數據

• eg1. delete from stu;
• eg2. delete from stu where id = “001”;

修改:update

修改數據

• eg1. update stu set age = 22;
• eg2. uodate stu set age = 20 where name = “李四”；

查詢:select

• 普通查詢：
  eg1. select * from stu;
  eg2. select id name sex age from stu;
  eg3. select name from stu where age > 20;
• 去重查詢：distinct
  eg. select distinct age from stu;
• 排序方式：order by asc|desc 升序|降序
  eg.select distinct age
  from stu
  order by age desc
• 分組查詢:group by
  select sid,SUM(score) all_score
  from result
  group by sid;
• 多表查詢：
  eg.查詢年齡小於二十歲的學生不及格信息
  • 等值查詢
    select name,score
    from stu,result
    where id = sid and age < 20 and score < 60;
• 連接查詢
  • 外連接查詢
    • 左外連接查詢
      select name,score
      from
      (select id,name from stu where age < 20) a
      left join
      (select sid,score from result where score < 60) b
      on id= sid
      where score is not null;
    • 右外連接查詢
      select name,score
      from
      (select id,name from stu where age < 20) a
      right join
      (select sid,score from result where score < 60) b
      on id= sid
      where name is not null;
    • 全外連接查詢
      select name,score
      from
      (select id,name from stu where age < 20) a
      full join
      (select sid,score from result where score < 60) b
      on id= sid
      where name is not null;
  • 內連接查詢
    select name,score
    from
    (select id,name from stu where age < 20) a
    inner join
    (select sid,score from result where score < 60) b
    on id= sid;
• 聯合查詢：union | union all
  select * from stu
  union all
  select * from teach;