sql函数

if()
使用：
if(判断条件,是的话等于什么值，不是的话等于什么值)
example：a是否等于3，是的话赋值为1，不是的话赋值为0

 if(a=3,1,0)

开窗函数：
rank() over (partition by 参数一order by 参数二 desc)
example：
原表：students表

students	grade	height
zhou	100	170
zhou	99	168
zhou	98	168
zhou	98	167
zhang	78	150
zhang	60	160
fu	70	153

select student，grade，rank() over (partition by students order by height desc) as sert from students;

现表：

students	grade	sert
zhou	100	1
zhou	99	2
zhou	98	2
zhou	98	4
zhang	60	1
zhang	78	2
fu	70	1

row_number() over (partition by 参数一order by 参数二 desc)
example：
原表：students表

students	grade	height
zhou	100	170
zhou	99	168
zhou	98	168
zhou	98	167
zhang	78	150
zhang	60	160
fu	70	153

select student，grade，row_number() over (partition by students order by height desc) as sert from students;

现表：

students	grade	sert
zhou	100	1
zhou	99	2
zhou	98	3
zhou	98	4
zhang	60	1
zhang	78	2
fu	70	1

dense_rank() over (partition by 参数一order by 参数二 desc)
example：
原表：students表

students	grade	height
zhou	100	170
zhou	99	168
zhou	98	168
zhou	98	167
zhang	78	150
zhang	60	160
fu	70	153

select student，grade，dense_rank() over (partition by students order by height desc) as sert from students;

现表：

students	grade	sert
zhou	100	1
zhou	99	2
zhou	98	2
zhou	98	3
zhang	60	1
zhang	78	2
fu	70	1