什么是buffer(sort)
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BUFFER (SORT)
Description
Performs a memory sort on a row source
Versions
This operation was introduced in Oracle 9.0.1 though it may have been used in limited circumstances in some earlier versions
This operation is implemented in the following versions
9.0.1 9.2.0
Examples
Example 1
This example was developed using Oracle 9.2.0.1 on Windows 2000
This example requires the following table and index definitions
CREATE TABLE t1 (c1 NUMBER);
CREATE INDEX T1_C1 ON T1(C1);
At least one of the tables must be analysed
ANALYZE TABLE t1 COMPUTE STATISTICS;
The statement
SELECT t1.c01, t2.c01
FROM t1;
generates the following execution plan
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 MERGE JOIN (CARTESIAN)
2 1 TABLE ACCESS (FULL) OF 'T1'
3 1 BUFFER (SORT)
4 3 TABLE ACCESS (FULL) OF 'T2'
Example 2
This example was developed using Oracle 9.2.0.1 on Windows 2000
This example requires the following table and index definitions
CREATE TABLE t1 (c1 NUMBER,c2 NUMBER);
In Oracle 9.0.1 and above the statement
SELECT c1,c2 FROM t1
CONNECT BY c1 = PRIOR c2
START WITH c1 = 0;
generates the following execution plan
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 CONNECT BY (WITH FILTERING)
2 1 NESTED LOOPS
3 2 TABLE ACCESS (FULL) OF 'T1'
4 2 TABLE ACCESS (BY USER ROWID) OF 'T1'
5 1 NESTED LOOPS
6 5 BUFFER (SORT)
7 6 CONNECT BY PUMP
8 5 TABLE ACCESS (FULL) OF 'T1'
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