SQL笔记

1.向表中添加数据：insert into table_name(col1,col2,...) values (data1,data2,...);

2.通过其他数据表向表中添加数据：insert into table_name(col1,col2,...)  select col1,col2,... from table_name2;

3.如果目标表不存在（即被导入数据的表不存在）：create table table_name as select col1,col2,col3,... from table_source;

4.更新表：update table_name set col1=data1,col2=data2,... [where condition];

5.删除表：delete from table_name [where condition];

6.添加主键约束（唯一且不为空）：alter table table_name add constraints constraint_name primary key (col_name);

   create table table_name(col_name1 type,col_name2 type,primary key (col_name));

7.添加外键约束（保证数据完整性、一致性）： create table table_name(col_name1 type,col_name2 type,primary key (col_name)，constraint  fk_name foreign key (col_name) references table_name(col_name) on delete cascade); on delete cascade 表示设置级联删除，当主键的字段被删除，外键所对应的字段也同时被删除。