todo el mundo:
Genial. Se cumple un pequeño requisito y se utilizan tres formas de escritura. El plan de ejecución es el siguiente:
SQL> SELECT DAY_ID,NAME,URL,CNT
2 FROM (SELECT DAY_ID,NAME,URL,CNT,row_number() OVER(PARTITION BY DAY_ID, NAME ORDER BY CNT DESC) RANK
3 FROM (SELECT T.DAY_ID,
4 T.NAME,
5 T.URL,
6 COUNT(1) CNT
7 FROM TEST T
8 GROUP BY T.DAY_ID, T.NAME, T.URL) d)
9 WHERE RANK=1;
执行计划
----------------------------------------------------------
Plan hash value: 481755404
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 22 | 1144 | 5 (40)| 00:00:01 |
|* 1 | VIEW | | 22 | 1144 | 5 (40)| 00:00:01 |
|* 2 | WINDOW SORT PUSHED RANK| | 22 | 572 | 5 (40)| 00:00:01 |
| 3 | HASH GROUP BY | | 22 | 572 | 5 (40)| 00:00:01 |
| 4 | TABLE ACCESS FULL | TEST | 22 | 572 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RANK"=1)
2 - filter(ROW_NUMBER() OVER ( PARTITION BY "T"."DAY_ID","T"."NAME"
ORDER BY COUNT(*) DESC )<=1)
Note
-----
- dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
7 consistent gets
0 physical reads
0 redo size
729 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
5 rows processed
SQL> SELECT DAY_ID,NAME,URL,CNT
2 FROM (SELECT T.DAY_ID,
3 T.NAME,
4 T.URL,
5 COUNT(1) CNT,
6 row_number() OVER(PARTITION BY T.DAY_ID,T.NAME ORDER BY COUNT(1) DESC) RANK
7 FROM TEST T
8 GROUP BY T.DAY_ID,
9 T.NAME,
10 T.URL)
11 WHERE RANK=1;
执行计划
----------------------------------------------------------
Plan hash value: 481755404
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 22 | 1144 | 5 (40)| 00:00:01 |
|* 1 | VIEW | | 22 | 1144 | 5 (40)| 00:00:01 |
|* 2 | WINDOW SORT PUSHED RANK| | 22 | 572 | 5 (40)| 00:00:01 |
| 3 | HASH GROUP BY | | 22 | 572 | 5 (40)| 00:00:01 |
| 4 | TABLE ACCESS FULL | TEST | 22 | 572 | 3 (0)| 00:00:01 |
---------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RANK"=1)
2 - filter(ROW_NUMBER() OVER ( PARTITION BY "T"."DAY_ID","T"."NAME"
ORDER BY COUNT(*) DESC )<=1)
Note
-----
- dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
7 consistent gets
0 physical reads
0 redo size
729 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
5 rows processed
SQL> SELECT DAY_ID,NAME,URL,cnt
2 FROM (SELECT T.DAY_ID,
3 T.NAME,
4 T.URL,
5 COUNT(1) cnt,
6 MAX(COUNT(1)) OVER(PARTITION BY DAY_ID,NAME) cnt1
7 FROM TEST T
8 GROUP BY T.DAY_ID, T.NAME, T.URL) d
9 WHERE cnt=cnt1;
执行计划
----------------------------------------------------------
Plan hash value: 1133560901
-----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 22 | 1144 | 4 (25)| 00:00:01 |
|* 1 | VIEW | | 22 | 1144 | 4 (25)| 00:00:01 |
| 2 | WINDOW BUFFER | | 22 | 572 | 4 (25)| 00:00:01 |
| 3 | SORT GROUP BY | | 22 | 572 | 4 (25)| 00:00:01 |
| 4 | TABLE ACCESS FULL| TEST | 22 | 572 | 3 (0)| 00:00:01 |
-----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("CNT"="CNT1")
Note
-----
- dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
7 consistent gets
0 physical reads
0 redo size
729 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
5 rows processed
SQL> spool off;
Se puede ver que el primer tipo de escritura es esencialmente el mismo que el segundo tipo, el tercer tipo de escritura está más ordenado en la memoria y el efecto es un poco pobre.