Java代碼
KEEP
看到很多人對於keep不理解，這裡解釋一下！
Returns the row ranked first using DENSE_RANK
2種取值：
DENSE_RANK FIRST
DENSE_RANK LAST
在keep (DENSE_RANK first ORDER BY sl) 結果集中再取max、min的例子。
SQL> select * from test;
ID MC SL
——————– ——————– ——————-
1 111 1
1 222 1
1 333 2
1 555 3
1 666 3
2 111 1
2 222 1
2 333 2
2 555 2
9 rows selected
SQL>
SQL> select id,mc,sl,
2 min(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id),
3 max(mc) keep (DENSE_RANK last ORDER BY sl) over(partition by id)
4 from test
5 ;
ID MC SL MIN(MC)KEEP(DENSE_RANKFIRSTORD MAX(MC)KEEP(DENSE_RANKLASTORDE
——————– ——————– ——————- —————————— ——————————
1 111 1 111 666
1 222 1 111 666
1 333 2 111 666
1 555 3 111 666
1 666 3 111 666
2 111 1 111 555
2 222 1 111 555
2 333 2 111 555
2 555 2 111 555
9 rows selected
SQL>
不要混淆keep內（first、last）外（min、max或者其他）：
min是可以對應last的
max是可以對應first的
SQL> select id,mc,sl,
2 min(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id),
3 max(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id),
4 min(mc) keep (DENSE_RANK last ORDER BY sl) over(partition by id),
5 max(mc) keep (DENSE_RANK last ORDER BY sl) over(partition by id)
6 from test
7 ;
ID MC SL MIN(MC)KEEP(DENSE_RANKFIRSTORD MAX(MC)KEEP(DENSE_RANKFIRSTORD MIN(MC)KEEP(DENSE_RANKLASTORDE MAX(MC)KEEP(DENSE_RANKLASTORDE
——————– ——————– ——————- —————————— —————————— —————————— ——————————
1 111 1 111 222 555 666
1 222 1 111 222 555 666
1 333 2 111 222 555 666
1 555 3 111 222 555 666
1 666 3 111 222 555 666
2 111 1 111 222 333 555
2 222 1 111 222 333 555
2 333 2 111 222 333 555
2 555 2 111 222 333 555
9 rows selected
SQL> select id,mc,sl,
2 min(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id),
3 max(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id),
4 min(mc) keep (DENSE_RANK last ORDER BY sl) over(partition by id),
5 max(mc) keep (DENSE_RANK last ORDER BY sl) over(partition by id)
6 from test
7 ;
ID MC SL MIN(MC)KEEP(DENSE_RANKFIRSTORD MAX(MC)KEEP(DENSE_RANKFIRSTORD MIN(MC)KEEP(DENSE_RANKLASTORDE MAX(MC)KEEP(DENSE_RANKLASTORDE
——————– ——————– ——————- —————————— —————————— —————————— ——————————
1 111 1 111 222 555 666
1 222 1 111 222 555 666
1 333 2 111 222 555 666
1 555 3 111 222 555 666
1 666 3 111 222 555 666
2 111 1 111 222 333 555
2 222 1 111 222 333 555
2 333 2 111 222 333 555
2 555 2 111 222 333 555
min(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id)：id等於1的數量最小的（DENSE_RANK first ）為
1 111 1
1 222 1
在這個結果中取min(mc) 就是111
max(mc) keep (DENSE_RANK first ORDER BY sl) over(partition by id)
取max(mc) 就是222；
min(mc) keep (DENSE_RANK last ORDER BY sl) over(partition by id)：id等於1的數量最大的（DENSE_RANK first ）為
1 555 3
1 666 3
在這個結果中取min(mc) 就是222，取max(mc)就是666
