SQL知識之視窗函式

3、排序視窗函式

4、切分視窗函式

5、偏移視窗函式

6、first_value() , last_value()

前言：視窗函式屬於sql的高階查詢功能，有些資料庫的低版本可能還不支援，如mysql5.7版本暫不支援，sql server是支援的。

1、視窗函式的簡單介紹

2、累計計算視窗函式

2.1 普通累計

# 以年為分組，按月份累加計算營業額

select
month
,		amount,
sum(amount)
over
(partition
byyear
order
bymonth
)from trade

rows

between
unbounded
preceding
andcurrent
row# 包括本行和之前的所有行
rows
between
3preceding
andcurrent
row# 包括本行以內和前三行
rows
between
current
rowand
unbounded
following
# 包括本行和之後所有的行
rows
between
3preceding
and1
following
#  從前三行到下一行
# 以年為分組，移動的累計求近三個月營業額的情況
select
month
,		amount,
sum(amount)
over
(partition
byyear
order
bymonth
rows
between
2preceding
andcurrent
row)
from trade

3.1 row_number()

select*,

row_number(
)over
(partition
by goods order
by trade_date desc
)as rank
from trade

select*,

rank(
)over
(partition
by goods order
by trade_date desc
)as rank
from trade

select*,

dense_rank(
)over
(partition
by goods order
by trade_date desc
)as rank
from trade

# 將支付金額按順序分成5份，即分成5個等級

select*,
ntilt(5)
over
(partition
by goods order
by amount desc)as
level
from trade

5.1 lag()

select id,

lag(name,
1, name)
over
(order
by id)
as lag_name
from person

select id,

lead(name,
1, name)
over
(order
by id)
as lead_name
from person

6.1 first_value()

select id,

first_value(url)
over
(partition
by cookieid order
by createtime)
as first1
from person

select id,

last_value(url)
over
(partition
by cookieid order
by createtime)
as last1
from person

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