使用with子句優化程式碼中重複查詢
/*
好處： 1. 效能更好，一份複製（類似SYS_TMP...)，多份使用。
2. 結構清晰，預先定義。
3. 程式碼修改不必修改多處。
請注意觀察語句1和語句2執行計劃的差異，尤其是語句2的SYS_TEMP_0FD9D6605_3B91BA4這些奇怪的命名。其實這就表示是
複製在記憶體中的資料，一次複製，多次使用。
*/
drop table t_with;
CREATE TABLE T_WITH AS SELECT ROWNUM ID, A.* FROM DBA_SOURCE A WHERE ROWNUM < 100001;
SET autotrace traceonly
Set linesize 1000
--語句1
SELECT ID, NAME FROM T_WITH
WHERE ID IN
(SELECT MAX(ID) FROM T_WITH
UNION ALL
SELECT MIN(ID) FROM T_WITH
UNION ALL
SELECT TRUNC(AVG(ID)) FROM T_WITH);
執行計劃
----------------------------------------------------------------------------------
Plan hash value: 647530712
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 3 | 129 | 1382 (1)| 00:00:17 |
|* 1 | HASH JOIN | | 3 | 129 | 1382 (1)| 00:00:17 |
| 2 | VIEW | VW_NSO_1 | 3 | 39 | 1035 (1)| 00:00:13 |
| 3 | HASH UNIQUE | | 3 | 39 | 1035 (67)| 00:00:13 |
| 4 | UNION-ALL | | | | | |
| 5 | SORT AGGREGATE | | 1 | 13 | | |
| 6 | TABLE ACCESS FULL| T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
| 7 | SORT AGGREGATE | | 1 | 13 | | |
| 8 | TABLE ACCESS FULL| T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
| 9 | SORT AGGREGATE | | 1 | 13 | | |
| 10 | TABLE ACCESS FULL| T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
| 11 | TABLE ACCESS FULL | T_WITH | 91060 | 2667K| 345 (1)| 00:00:05 |
-----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("ID"="MAX(ID)")
Note
-----
- dynamic sampling used for this statement (level=2)
統計資訊
----------------------------------------------------------
0 recursive calls
0 db block gets
4969 consistent gets
0 physical reads
0 redo size
558 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
3 rows processed
--語句2
WITH AGG AS (SELECT MAX(ID) MAX, MIN(ID) MIN, TRUNC(AVG(ID)) AVG FROM T_WITH)
SELECT ID, NAME FROM T_WITH
WHERE ID IN
( SELECT MAX FROM AGG UNION ALL SELECT MIN FROM AGG UNION ALL SELECT AVG FROM AGG);
執行計劃
--------------------------------------------------------------------------------------------------------
Plan hash value: 3705751949
---------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 3 | 129 | 697 (1)| 00:00:09 |
| 1 | TEMP TABLE TRANSFORMATION | | | | | |
| 2 | LOAD AS SELECT | SYS_TEMP_0FD9D6605_3B91BA4 | | | | |
| 3 | SORT AGGREGATE | | 1 | 13 | | |
| 4 | TABLE ACCESS FULL | T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
|* 5 | HASH JOIN | | 3 | 129 | 352 (1)| 00:00:05 |
| 6 | VIEW | VW_NSO_1 | 3 | 39 | 6 (0)| 00:00:01 |
| 7 | HASH UNIQUE | | 3 | 39 | 6 (67)| 00:00:01 |
| 8 | UNION-ALL | | | | | |
| 9 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
| 10 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6605_3B91BA4 | 1 | 13 | 2 (0)| 00:00:01 |
| 11 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
| 12 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6605_3B91BA4 | 1 | 13 | 2 (0)| 00:00:01 |
| 13 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
| 14 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6605_3B91BA4 | 1 | 13 | 2 (0)| 00:00:01 |
| 15 | TABLE ACCESS FULL | T_WITH | 91060 | 2667K| 345 (1)| 00:00:05 |
---------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("ID"="MAX")
Note
-----
- dynamic sampling used for this statement (level=2)
統計資訊
----------------------------------------------------------
2 recursive calls
8 db block gets
2496 consistent gets
1 physical reads
600 redo size
558 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
3 rows processed
好處： 1. 效能更好，一份複製（類似SYS_TMP...)，多份使用。
2. 結構清晰，預先定義。
3. 程式碼修改不必修改多處。
請注意觀察語句1和語句2執行計劃的差異，尤其是語句2的SYS_TEMP_0FD9D6605_3B91BA4這些奇怪的命名。其實這就表示是
複製在記憶體中的資料，一次複製，多次使用。
*/
drop table t_with;
CREATE TABLE T_WITH AS SELECT ROWNUM ID, A.* FROM DBA_SOURCE A WHERE ROWNUM < 100001;
SET autotrace traceonly
Set linesize 1000
--語句1
SELECT ID, NAME FROM T_WITH
WHERE ID IN
(SELECT MAX(ID) FROM T_WITH
UNION ALL
SELECT MIN(ID) FROM T_WITH
UNION ALL
SELECT TRUNC(AVG(ID)) FROM T_WITH);
執行計劃
----------------------------------------------------------------------------------
Plan hash value: 647530712
-----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 3 | 129 | 1382 (1)| 00:00:17 |
|* 1 | HASH JOIN | | 3 | 129 | 1382 (1)| 00:00:17 |
| 2 | VIEW | VW_NSO_1 | 3 | 39 | 1035 (1)| 00:00:13 |
| 3 | HASH UNIQUE | | 3 | 39 | 1035 (67)| 00:00:13 |
| 4 | UNION-ALL | | | | | |
| 5 | SORT AGGREGATE | | 1 | 13 | | |
| 6 | TABLE ACCESS FULL| T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
| 7 | SORT AGGREGATE | | 1 | 13 | | |
| 8 | TABLE ACCESS FULL| T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
| 9 | SORT AGGREGATE | | 1 | 13 | | |
| 10 | TABLE ACCESS FULL| T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
| 11 | TABLE ACCESS FULL | T_WITH | 91060 | 2667K| 345 (1)| 00:00:05 |
-----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("ID"="MAX(ID)")
Note
-----
- dynamic sampling used for this statement (level=2)
統計資訊
----------------------------------------------------------
0 recursive calls
0 db block gets
4969 consistent gets
0 physical reads
0 redo size
558 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
3 rows processed
--語句2
WITH AGG AS (SELECT MAX(ID) MAX, MIN(ID) MIN, TRUNC(AVG(ID)) AVG FROM T_WITH)
SELECT ID, NAME FROM T_WITH
WHERE ID IN
( SELECT MAX FROM AGG UNION ALL SELECT MIN FROM AGG UNION ALL SELECT AVG FROM AGG);
執行計劃
--------------------------------------------------------------------------------------------------------
Plan hash value: 3705751949
---------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 3 | 129 | 697 (1)| 00:00:09 |
| 1 | TEMP TABLE TRANSFORMATION | | | | | |
| 2 | LOAD AS SELECT | SYS_TEMP_0FD9D6605_3B91BA4 | | | | |
| 3 | SORT AGGREGATE | | 1 | 13 | | |
| 4 | TABLE ACCESS FULL | T_WITH | 91060 | 1156K| 345 (1)| 00:00:05 |
|* 5 | HASH JOIN | | 3 | 129 | 352 (1)| 00:00:05 |
| 6 | VIEW | VW_NSO_1 | 3 | 39 | 6 (0)| 00:00:01 |
| 7 | HASH UNIQUE | | 3 | 39 | 6 (67)| 00:00:01 |
| 8 | UNION-ALL | | | | | |
| 9 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
| 10 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6605_3B91BA4 | 1 | 13 | 2 (0)| 00:00:01 |
| 11 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
| 12 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6605_3B91BA4 | 1 | 13 | 2 (0)| 00:00:01 |
| 13 | VIEW | | 1 | 13 | 2 (0)| 00:00:01 |
| 14 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6605_3B91BA4 | 1 | 13 | 2 (0)| 00:00:01 |
| 15 | TABLE ACCESS FULL | T_WITH | 91060 | 2667K| 345 (1)| 00:00:05 |
---------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("ID"="MAX")
Note
-----
- dynamic sampling used for this statement (level=2)
統計資訊
----------------------------------------------------------
2 recursive calls
8 db block gets
2496 consistent gets
1 physical reads
600 redo size
558 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
3 rows processed
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/29135257/viewspace-2093848/，如需轉載，請註明出處，否則將追究法律責任。
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