组合查询

union 在查询的过程中自动的去掉了重复的行，

WX20190524-225713@2x.png

union all会显示所有的结果

WX20190524-230055@2x.png

插入数据

insert into table_name(...) values(...);

复制表

select *
into table_name_copy
from table_name;

create table table_name_copy as
select * from table_name;

更新

update table_name
set table_column_name = ...
where table_column_name_2 = ...;

删除

delete from table_name
where ...;

创建表

create table table_name
(
table_column_name_1  data_type_1 null,
table_column_name 2   data_type_2 not null
);

更新表

alter table table_name
add new_table_column_name data_type;

alter table table_name
drop column table_column_name;

drop table table_name;

创建视图

create view view_name as
select ...;