OVER(PARTITION BY)函數介紹
Oracle從8.1.6開始提供分析函數，分析函數用於計算基於組的某種聚合值，它和聚合函數的不同之處是：對於每個組返回多行，而聚合函數對於每個組只返回一行。
開窗函數指定了分析函數工作的數據窗口大小，這個數據窗口大小可能會隨着行的變化而變化，舉例如下：
1：over后的寫法：
over（order by salary） 按照salary排序進行累計，order by是個默認的開窗函數
over（partition by deptno）按照部門分區
2：開窗的窗口范圍：
over（order by salary range between 5 preceding and 5 following）：窗口范圍為當前行數據幅度減5加5后的范圍內的。
舉例：
--sum(s)over(order by s range between 2 preceding and 2 following) 表示加2或2的范圍內的求和
select name,class,s, sum(s)over(order by s range between 2 preceding and 2 following) mm from t2adf 3 45 45 --45加2減2即43到47，但是s在這個范圍內只有45
asdf 3 55 55
cfe 2 74 74
3dd 3 78 158 --78在76到80范圍內有78，80，求和得158
fda 1 80 158
gds 2 92 92
ffd 1 95 190
dss 1 95 190
ddd 3 99 198
gf 3 99 198
舉例：
select name,class,s, sum(s)over(order by s rows between 2 preceding and 2 following) mm from t2
adf 3 45 174 （45+55+74=174）
asdf 3 55 252 （45+55+74+78=252）
cfe 2 74 332 （74+55+45+78+80=332）
3dd 3 78 379 （78+74+55+80+92=379）
fda 1 80 419
gds 2 92 440
ffd 1 95 461
dss 1 95 480
ddd 3 99 388
gf 3 99 293
3、與over函數結合的幾個函數介紹
下面以班級成績表t2來說明其應用
t2表信息如下：cfe 2 74
dss 1 95
ffd 1 95
fda 1 80
gds 2 92
gf 3 99
ddd 3 99
adf 3 45
asdf 3 55
3dd 3 78
select * from
(
select name,class,s,rank()over(partition by class order by s desc) mm from t2
)
where mm=1；
得到的結果是:
dss 1 95 1
ffd 1 95 1
gds 2 92 1
gf 3 99 1
ddd 3 99 1
注意：
1.在求第一名成績的時候，不能用row_number()，因為如果同班有兩個並列第一，row_number()只返回一個結果;
select * from
(
select name,class,s,row_number()over(partition by class order by s desc) mm from t2
)
where mm=1；
1 95 1 --95有兩名但是只顯示一個
2 92 1
3 99 1 --99有兩名但也只顯示一個
2.rank()和dense_rank()可以將所有的都查找出來：
如上可以看到采用rank可以將並列第一名的都查找出來；
rank()和dense_rank()區別：
--rank()是跳躍排序，有兩個第二名時接下來就是第四名；
select name,class,s,rank()over(partition by class order by s desc) mm from t2
dss 1 95 1
ffd 1 95 1
fda 1 80 3 --直接就跳到了第三
gds 2 92 1
cfe 2 74 2
gf 3 99 1
ddd 3 99 1
3dd 3 78 3
asdf 3 55 4
adf 3 45 5
--dense_rank()l是連續排序，有兩個第二名時仍然跟着第三名
select name,class,s,dense_rank()over(partition by class order by s desc) mm from t2
dss 1 95 1
ffd 1 95 1
fda 1 80 2 --連續排序（仍為2）
gds 2 92 1
cfe 2 74 2
gf 3 99 1
ddd 3 99 1
3dd 3 78 2
asdf 3 55 3
adf 3 45 4
--sum()over（）的使用
select name,class,s, sum(s)over(partition by class order by s desc) mm from t2 --根據班級進行分數求和
dss 1 95 190 --由於兩個95都是第一名，所以累加時是兩個第一名的相加
ffd 1 95 190
fda 1 80 270 --第一名加上第二名的
gds 2 92 92
cfe 2 74 166
gf 3 99 198
ddd 3 99 198
3dd 3 78 276
asdf 3 55 331
adf 3 45 376
first_value() over()和last_value() over()的使用
--找出這三條電路每條電路的第一條記錄類型和最后一條記錄類型
first_value(res_type) over(PARTITION BY opr_id ORDER BY res_type) low,
last_value(res_type) over(PARTITION BY opr_id ORDER BY res_type rows BETWEEN unbounded preceding AND unbounded following) high
FROM rm_circuit_route
WHERE opr_id IN ('000100190000000000021311','000100190000000000021355','000100190000000000021339')
ORDER BY opr_id;
注：rows BETWEEN unbounded preceding AND unbounded following 的使用
--取last_value時不使用rows BETWEEN unbounded preceding AND unbounded following的結果
first_value(res_type) over(PARTITION BY opr_id ORDER BY res_type) low,
last_value(res_type) over(PARTITION BY opr_id ORDER BY res_type) high
FROM rm_circuit_route
WHERE opr_id IN ('000100190000000000021311','000100190000000000021355','000100190000000000021339')
ORDER BY opr_id;
如下圖可以看到，如果不使用
取出該電路的第一條記錄，加上ignore nulls后，如果第一條是判斷的那個字段是空的，則默認取下一條，結果如下所示：
lag(expresstion,<offset>,<default>)
with a as
(select 1 id,'a' name from dual
union
select 2 id,'b' name from dual
union
select 3 id,'c' name from dual
union
select 4 id,'d' name from dual
union
select 5 id,'e' name from dual
)
select id,name, lag(id,1,'')over(order by name) from a;
--lead() over()函數用法（取出后N行數據）
lead(expresstion,<offset>,<default>)
with a as
(select 1 id,'a' name from dual
union
select 2 id,'b' name from dual
union
select 3 id,'c' name from dual
union
select 4 id,'d' name from dual
union
select 5 id,'e' name from dual
)
select id,name,lead(id,1,'')over(order by name) from a;
--ratio_to_report(a)函數用法 Ratio_to_report() 括號中就是分子，over() 括號中就是分母
with a as (select 1 a from dual
union all
select 1 a from dual
union all
select 1 a from dual
union all
select 2 a from dual
union all
select 3 a from dual
union all
select 4 a from dual
union all
select 4 a from dual
union all
select 5 a from dual
)
select a, ratio_to_report(a)over(partition by a) b from a
order by a;
with a as (select 1 a from dual
union all
select 1 a from dual
union all
select 1 a from dual
union all
select 2 a from dual
union all
select 3 a from dual
union all
select 4 a from dual
union all
select 4 a from dual
union all
select 5 a from dual
)
select a, ratio_to_report(a)over() b from a --分母缺省就是整個占比
order by a;
with a as (select 1 a from dual
union all
select 1 a from dual
union all
select 1 a from dual
union all
select 2 a from dual
union all
select 3 a from dual
union all
select 4 a from dual
union all
select 4 a from dual
union all
select 5 a from dual
)
select a, ratio_to_report(a)over() b from a
group by a order by a;--分組后的占比