Oracle 12CR2查询转换教程之临时表转换详解

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前言

大家都知道在12CR2中出现一种新的查询转换技术临时表转换，在下面的例子中，数据库对customers表上的子查询结果物化到一个临时表中:

SQL> show parameter star_transformation_enabled
star_transformation_enabled   string  FALSE
SQL> alter session set star_transformation_enabled='true';

Session altered.

SQL> SELECT c.cust_city,
 2 t.calendar_quarter_desc,
 3 SUM(s.amount_sold) sales_amount
 4 FROM sales s,
 5 times t,
 6 customers c,
 7 channels ch
 8 WHERE s.time_id = t.time_id
 9 AND s.cust_id = c.cust_id
 10 AND s.channel_id = ch.channel_id
 11 AND c.cust_state_province = 'CA'
 12 AND ch.channel_desc = 'Internet'
 13 AND t.calendar_quarter_desc IN ('1999-01','1999-02')
 14 GROUP BY c.cust_city, t.calendar_quarter_desc;
Montara      1999-02  1618.01
Pala       1999-01  3263.93
Cloverdale      1999-01  52.64
Cloverdale      1999-02  266.28
San Francisco     1999-01  3058.27
San Mateo      1999-01  8754.59
Los Angeles     1999-01  1886.19
San Mateo      1999-02  21399.42
Pala       1999-02  936.62
El Sobrante     1999-02  3744.03
El Sobrante     1999-01  5392.34
Quartzhill      1999-01  987.3
Legrand      1999-01  26.32
Pescadero      1999-01  26.32
Arbuckle      1999-02  241.2
Quartzhill      1999-02  412.83
Montara      1999-01  289.07
Arbuckle      1999-01  270.08
San Francisco     1999-02  11257
Los Angeles     1999-02  2128.59
Pescadero      1999-02  298.44
Legrand      1999-02  18.66

22 rows selected.

优化器使用临时表SYS_TEMP_0FD9D6893_63D6F82来代替customers表，并且使用临时表中的相关列来替换所引用的列cust_id和cust_city。数据库创建带有两列(c0 number,c1 varchar2(30))的临时表(从执行计划中的 6 – (rowset=256) “C0″[NUMBER,22], “C1″[VARCHAR2,30]也可以看到)。这些列关联到customers表中的cust_id和cust_city列。

在下面的执行计划中的1,2,3行物化customers子查询到临时表中，在第6行，数据库扫描临时表(代替子查询)来从事实表中构建位图。第27行扫描临时表执行连接返回代替扫描customers表。数据库不用对临时表应用customer表上的过滤条件，因为在物化临时表时已经应用了过滤条件。

SQL> select * from table(dbms_xplan.display_cursor(null,null,'advanced allstats last runstats_last peeked_binds'));
SQL_ID a069wzk60bbqd, child number 2
-------------------------------------
SELECT c.cust_city, t.calendar_quarter_desc, SUM(s.amount_sold)
sales_amount FROM sales s, times t, customers c, channels ch WHERE
s.time_id = t.time_id AND s.cust_id = c.cust_id AND s.channel_id =
ch.channel_id AND c.cust_state_province = 'CA' AND ch.channel_desc =
'Internet' AND t.calendar_quarter_desc IN ('1999-01','1999-02') GROUP
BY c.cust_city, t.calendar_quarter_desc

Plan hash value: 2164696140

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation       | Name      | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | Pstart| Pstop | A-Rows | A-Time | Buffers | Reads | Writes | OMem | 1Mem | Used-Mem |
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT     |       |  1 |  |  | 1177 (100)|   |  |  |  22 |00:00:00.25 | 9080 |  86 |  10 |  |  |   |
| 1 | TEMP TABLE TRANSFORMATION   |       |  1 |  |  |   |   |  |  |  22 |00:00:00.25 | 9080 |  86 |  10 |  |  |   |
| 2 | LOAD AS SELECT     | SYS_TEMP_0FD9D6893_63D6F82 |  1 |  |  |   |   |  |  |  0 |00:00:00.04 | 1535 |  0 |  10 | 1042K| 1042K|   |
|* 3 | TABLE ACCESS FULL    | CUSTOMERS     |  1 | 3341 | 86866 | 423 (1)| 00:00:01 |  |  | 3341 |00:00:00.01 | 1522 |  0 |  0 |  |  |   |
| 4 | HASH GROUP BY     |       |  1 | 877 | 49989 | 754 (1)| 00:00:01 |  |  |  22 |00:00:00.20 | 7538 |  85 |  0 | 1022K| 1022K| 1349K (0)|
|* 5 | HASH JOIN      |       |  1 | 14534 | 809K| 753 (1)| 00:00:01 |  |  | 964 |00:00:00.20 | 7538 |  85 |  0 | 1572K| 1572K| 1696K (0)|
| 6 |  TABLE ACCESS FULL    | SYS_TEMP_0FD9D6893_63D6F82 |  1 | 3341 | 50115 |  4 (0)| 00:00:01 |  |  | 3341 |00:00:00.01 |  18 |  10 |  0 |  |  |   |
|* 7 |  HASH JOIN      |       |  1 | 14534 | 596K| 749 (1)| 00:00:01 |  |  | 964 |00:00:00.19 | 7520 |  75 |  0 | 1538K| 1538K| 1685K (0)|
|* 8 |  TABLE ACCESS FULL    | TIMES      |  1 | 181 | 2896 | 18 (0)| 00:00:01 |  |  | 181 |00:00:00.01 |  65 |  0 |  0 |  |  |   |
| 9 |  VIEW       | VW_ST_A3F94988    |  1 | 14534 | 369K| 731 (1)| 00:00:01 |  |  | 964 |00:00:00.18 | 7455 |  75 |  0 |  |  |   |
| 10 |  NESTED LOOPS     |       |  1 | 14534 | 809K| 706 (1)| 00:00:01 |  |  | 964 |00:00:00.18 | 7455 |  75 |  0 |  |  |   |
| 11 |  PARTITION RANGE SUBQUERY |       |  1 | 14534 | 397K| 353 (0)| 00:00:01 |KEY(SQ)|KEY(SQ)| 964 |00:00:00.17 | 7271 |  75 |  0 |  |  |   |
| 12 |   BITMAP CONVERSION TO ROWIDS|       |  2 | 14534 | 397K| 353 (0)| 00:00:01 |  |  | 964 |00:00:00.16 | 7204 |  75 |  0 |  |  |   |
| 13 |   BITMAP AND    |       |  2 |  |  |   |   |  |  |  2 |00:00:00.16 | 7204 |  75 |  0 |  |  |   |
| 14 |   BITMAP MERGE    |       |  2 |  |  |   |   |  |  |  2 |00:00:00.02 |  15 |  5 |  0 | 1024K| 512K| 4096 (0)|
| 15 |   BITMAP KEY ITERATION |       |  2 |  |  |   |   |  |  |  2 |00:00:00.02 |  15 |  5 |  0 |  |  |   |
| 16 |    BUFFER SORT   |       |  2 |  |  |   |   |  |  |  2 |00:00:00.01 |  9 |  0 |  0 | 73728 | 73728 |   |
|* 17 |    TABLE ACCESS FULL  | CHANNELS     |  1 |  1 | 13 |  3 (0)| 00:00:01 |  |  |  1 |00:00:00.01 |  9 |  0 |  0 |  |  |   |
|* 18 |    BITMAP INDEX RANGE SCAN| SALES_CHANNEL_BIX   |  2 |  |  |   |   |KEY(SQ)|KEY(SQ)|  2 |00:00:00.02 |  6 |  5 |  0 |  |  |   |
| 19 |   BITMAP MERGE    |       |  2 |  |  |   |   |  |  |  2 |00:00:00.02 |  445 |  9 |  0 | 1024K| 512K|39936 (0)|
| 20 |   BITMAP KEY ITERATION |       |  2 |  |  |   |   |  |  | 181 |00:00:00.02 |  445 |  9 |  0 |  |  |   |
| 21 |    BUFFER SORT   |       |  2 |  |  |   |   |  |  | 362 |00:00:00.01 |  65 |  0 |  0 | 73728 | 73728 |   |
|* 22 |    TABLE ACCESS FULL  | TIMES      |  1 | 181 | 2896 | 18 (0)| 00:00:01 |  |  | 181 |00:00:00.01 |  65 |  0 |  0 |  |  |   |
|* 23 |    BITMAP INDEX RANGE SCAN| SALES_TIME_BIX    | 362 |  |  |   |   |KEY(SQ)|KEY(SQ)| 181 |00:00:00.02 |  380 |  9 |  0 |  |  |   |
| 24 |   BITMAP MERGE    |       |  2 |  |  |   |   |  |  |  2 |00:00:00.13 | 6744 |  61 |  0 | 1024K| 512K|45056 (0)|
| 25 |   BITMAP KEY ITERATION |       |  2 |  |  |   |   |  |  | 403 |00:00:00.12 | 6744 |  61 |  0 |  |  |   |
| 26 |    BUFFER SORT   |       |  2 |  |  |   |   |  |  | 6682 |00:00:00.01 |  18 |  0 |  0 | 5512K| 964K| 174K (0)|
| 27 |    TABLE ACCESS FULL  | SYS_TEMP_0FD9D6893_63D6F82 |  1 | 3341 | 16705 |  4 (0)| 00:00:01 |  |  | 3341 |00:00:00.01 |  18 |  0 |  0 |  |  |   |
|* 28 |    BITMAP INDEX RANGE SCAN| SALES_CUST_BIX    | 6682 |  |  |   |   |KEY(SQ)|KEY(SQ)| 403 |00:00:00.10 | 6726 |  61 |  0 |  |  |   |
| 29 |  TABLE ACCESS BY USER ROWID | SALES      | 964 |  1 | 29 | 378 (0)| 00:00:01 | ROWID | ROWID | 964 |00:00:00.01 |  184 |  0 |  0 |  |  |   |
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------

 1 - SEL$D5EF7599
 2 - SEL$F6045C7B
 3 - SEL$F6045C7B / C@SEL$F6045C7B
 6 - SEL$D5EF7599 / T1@SEL$9C741BEB
 8 - SEL$D5EF7599 / T@SEL$1
 9 - SEL$5E9A798F / VW_ST_A3F94988@SEL$D5EF7599
 10 - SEL$5E9A798F
 12 - SEL$5E9A798F / S@SEL$1
 17 - SEL$6EE793B7 / CH@SEL$6EE793B7
 22 - SEL$ACF30367 / T@SEL$ACF30367
 27 - SEL$E1F9C76C / T1@SEL$E1F9C76C
 29 - SEL$5E9A798F / SYS_CP_S@SEL$5E9A798F

Outline Data
-------------

 /*+
  BEGIN_OUTLINE_DATA
  IGNORE_OPTIM_EMBEDDED_HINTS
  OPTIMIZER_FEATURES_ENABLE('12.2.0.1')
  DB_VERSION('12.2.0.1')
  OPT_PARAM('star_transformation_enabled' 'true')
  ALL_ROWS
  NO_PARALLEL
  OUTLINE_LEAF(@"SEL$F6045C7B")
  OUTLINE_LEAF(@"SEL$ACF30367")
  OUTLINE_LEAF(@"SEL$6EE793B7")
  OUTLINE_LEAF(@"SEL$E1F9C76C")
  OUTLINE_LEAF(@"SEL$5E9A798F")
  TABLE_LOOKUP_BY_NL(@"SEL$0E028FD0" "S"@"SEL$1")
  OUTLINE_LEAF(@"SEL$D5EF7599")
  OUTLINE(@"SEL$1")
  OUTLINE(@"SEL$0E028FD0")
  OUTLINE(@"SEL$C3AF6D21")
  ELIMINATE_JOIN(@"SEL$1" "CH"@"SEL$1")
  OUTLINE(@"SEL$5208623C")
  STAR_TRANSFORMATION(@"SEL$1" "S"@"SEL$1" SUBQUERIES(("T"@"SEL$1") ("CH"@"SEL$1") TEMP_TABLE("C"@"SEL$1")))
  FULL(@"SEL$D5EF7599" "T"@"SEL$1")
  NO_ACCESS(@"SEL$D5EF7599" "VW_ST_A3F94988"@"SEL$D5EF7599")
  FULL(@"SEL$D5EF7599" "T1"@"SEL$9C741BEB")
  LEADING(@"SEL$D5EF7599" "T"@"SEL$1" "VW_ST_A3F94988"@"SEL$D5EF7599" "T1"@"SEL$9C741BEB")
  USE_HASH(@"SEL$D5EF7599" "VW_ST_A3F94988"@"SEL$D5EF7599")
  USE_HASH(@"SEL$D5EF7599" "T1"@"SEL$9C741BEB")
  SWAP_JOIN_INPUTS(@"SEL$D5EF7599" "T1"@"SEL$9C741BEB")
  USE_HASH_AGGREGATION(@"SEL$D5EF7599")
  BITMAP_AND(@"SEL$5E9A798F" "S"@"SEL$1" ("SALES"."CHANNEL_ID") 1)
  BITMAP_AND(@"SEL$5E9A798F" "S"@"SEL$1" ("SALES"."TIME_ID") 2)
  BITMAP_AND(@"SEL$5E9A798F" "S"@"SEL$1" ("SALES"."CUST_ID") 3)
  ROWID(@"SEL$5E9A798F" "SYS_CP_S"@"SEL$5E9A798F")
  LEADING(@"SEL$5E9A798F" "S"@"SEL$1" "SYS_CP_S"@"SEL$5E9A798F")
  SUBQUERY_PRUNING(@"SEL$5E9A798F" "S"@"SEL$1" PARTITION)
  USE_NL(@"SEL$5E9A798F" "SYS_CP_S"@"SEL$5E9A798F")
  FULL(@"SEL$E1F9C76C" "T1"@"SEL$E1F9C76C")
  SEMIJOIN_DRIVER(@"SEL$E1F9C76C")
  FULL(@"SEL$6EE793B7" "CH"@"SEL$6EE793B7")
  SEMIJOIN_DRIVER(@"SEL$6EE793B7")
  FULL(@"SEL$ACF30367" "T"@"SEL$ACF30367")
  SEMIJOIN_DRIVER(@"SEL$ACF30367")
  FULL(@"SEL$F6045C7B" "C"@"SEL$F6045C7B")
  SEMIJOIN_DRIVER(@"SEL$F6045C7B")
  END_OUTLINE_DATA
 */

Predicate Information (identified by operation id):
---------------------------------------------------

 3 - filter("C"."CUST_STATE_PROVINCE"='CA')
 5 - access("ITEM_1"="C0")
 7 - access("ITEM_2"="T"."TIME_ID")
 8 - filter(("T"."CALENDAR_QUARTER_DESC"='1999-01' OR "T"."CALENDAR_QUARTER_DESC"='1999-02'))
 17 - filter("CH"."CHANNEL_DESC"='Internet')
 18 - access("S"."CHANNEL_ID"="CH"."CHANNEL_ID")
 22 - filter(("T"."CALENDAR_QUARTER_DESC"='1999-01' OR "T"."CALENDAR_QUARTER_DESC"='1999-02'))
 23 - access("S"."TIME_ID"="T"."TIME_ID")
 28 - access("S"."CUST_ID"="C0")

Column Projection Information (identified by operation id):
-----------------------------------------------------------

 1 - "C1"[VARCHAR2,30], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7], SUM("ITEM_3")[22]
 2 - SYSDEF[4], SYSDEF[0], SYSDEF[1], SYSDEF[120], SYSDEF[0]
 3 - "C"."CUST_ID"[NUMBER,22], "C"."CUST_CITY"[VARCHAR2,30], "C"."CUST_STATE_PROVINCE"[VARCHAR2,40]
 4 - "C1"[VARCHAR2,30], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7], SUM("ITEM_3")[22]
 5 - (#keys=1; rowset=256) "C0"[NUMBER,22], "ITEM_1"[NUMBER,22], "C1"[VARCHAR2,30], "T"."TIME_ID"[DATE,7], "ITEM_2"[DATE,7], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7], "ITEM_3"[NUMBER,22]
 6 - (rowset=256) "C0"[NUMBER,22], "C1"[VARCHAR2,30]
 7 - (#keys=1; rowset=256) "T"."TIME_ID"[DATE,7], "ITEM_2"[DATE,7], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7], "ITEM_1"[NUMBER,22], "ITEM_3"[NUMBER,22]
 8 - (rowset=256) "T"."TIME_ID"[DATE,7], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7]
 9 - "ITEM_1"[NUMBER,22], "ITEM_2"[DATE,7], "ITEM_3"[NUMBER,22]
 10 - ROWID[ROWID,10], ROWID[ROWID,10], "S"."CUST_ID"[NUMBER,22], "S"."TIME_ID"[DATE,7], "S"."AMOUNT_SOLD"[NUMBER,22]
 11 - ROWID[ROWID,10]
 12 - ROWID[ROWID,10]
 13 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 32496]
 14 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 32496]
 15 - STRDEF[10], STRDEF[10], STRDEF[7920], "S"."CHANNEL_ID"[NUMBER,22]
 16 - (#keys=2) "CH"."CHANNEL_ID"[NUMBER,22], "CH"."CHANNEL_DESC"[VARCHAR2,20]
 17 - (rowset=256) "CH"."CHANNEL_ID"[NUMBER,22], "CH"."CHANNEL_DESC"[VARCHAR2,20]
 18 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 7920], "S"."CHANNEL_ID"[NUMBER,22]
 19 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 32496]
 20 - STRDEF[10], STRDEF[10], STRDEF[7920], "S"."TIME_ID"[DATE,7]
 21 - (#keys=2) "T"."TIME_ID"[DATE,7], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7]
 22 - (rowset=256) "T"."TIME_ID"[DATE,7], "T"."CALENDAR_QUARTER_DESC"[CHARACTER,7]
 23 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 7920], "S"."TIME_ID"[DATE,7]
 24 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 32496]
 25 - STRDEF[10], STRDEF[10], STRDEF[7920], "S"."CUST_ID"[NUMBER,22]
 26 - (#keys=1) "C0"[NUMBER,22]
 27 - (rowset=256) "C0"[NUMBER,22]
 28 - STRDEF[BM VAR, 10], STRDEF[BM VAR, 10], STRDEF[BM VAR, 7920], "S"."CUST_ID"[NUMBER,22]
 29 - ROWID[ROWID,10], "S"."CUST_ID"[NUMBER,22], "S"."TIME_ID"[DATE,7], "S"."AMOUNT_SOLD"[NUMBER,22]

Note
-----
 - automatic DOP: Computed Degree of Parallelism is 1 because of parallel threshold
 - cbqt star transformation used for this statement
 - this is an adaptive plan

总结

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