- select：选择
select * from table_name;
select distinct column_x from table_name; #distinct:去重
#选top
select top number column_name(s) from table_name; # top numer
select top percentage column_name(s) from table_name; # top percentage
select column_name(s) from table_name limit number; # limit
#min, max, avg, sum, count...
select min(column_x) from table_name;
select max(colums_x) from table_name;
- where：筛选
select column_0, column_1, ...
from table_name where condition;
# use like in condition
select column0, column1, ...
from table_name
where column_n like pattern; # '%':>=0 characters; '_':1 character
#in, between
where column_n in (...);
where column_n between value_1 and value2;
condition操作符：=, >, <, >=, <=, between, like, in, and, or, not
- order by:排序
select column1, column2, ...
from table_name
order by column1, column2, ... asc; #或dsc
- insert into：插入行
insert into table_name (column1, column2, column3, ...)
values (value1, value2, value3, ...);
insert into table_name values (value1, value2, value3, ...);
- update：修改行value
update table set column1=value1, column2=value2, ... where condition; #where语句：optional
6.delete：删除部分行
delete from table_name where condition;
where语句 optional，不选则为删除所有
7.as：重命名table或行
select column_x as col_x from table_name;
select column_x from table_name as tb;
8.join
- 一般join指inner join，交集；其他（left，right和full均为outer join）
-
各种join图示
SQL-Join.jpg - self join：通常用于同一个表不同行之间的关系
select column_x
from table_name tb_1, table_name tb_2
where condition;
9.union：用于合并两个或多个 SELECT 语句的结果集，默认去重，不去重用union all
select column_name(s) from table_name1
union
select column_name(s) from table_name2;
10.group by:根据一个或多个列对结果集进行分组
#eg: 得到不同国家对应的用户总数
select count(customer_id), country
from customers
group by country;
11.having：having和where均引导条件语句，但是区别是having是：在查询返回结果集以后对查询结果进行的过滤操作，支持聚合操作（avg，count等），where约束来自数据库的数据。
# 筛选平均工资高于3000的部门
select deparment, avg(salary) as average from salary_info
group by deparment having average > 3000
12.exists: 在遍历每一条记录时，exists 后值为true，则将该条记录加入；否则不加入
select column(s) from table_name where exists(...)
**exists和in的区别 https://www.jianshu.com/p/f212527d76ff **
- any, all:引导一个范围，限定operator比较的范围
select column(s) from table_name
where column operator all (select column_name from table_name where condition);
#operator：>, <, =, ...
14.select into:存储为新的表
select column(s) into new_tabbe [in externalDB]
from old_table where condition;
15.case:类似c语言的case
case
when condition_0 then res_0
when condition_1 then res_1
...
(else res_1)
end
16.null的处理
#eg:ifnull是mysql的用法，对应还有isnull（sql server）
select column1 * ifnull(column2, 0)
from table_name
17.procedure
#create
create procedure_name
as
sql statement
go
#execute
exec procedure_name
#带参数的例子
create select_stu @city nvarchar(30), @habit nvarchar(30)
as
select * from student where city = @city and habit = @habit
go;
exec select_stu city="beijing", habit="reading"
