MERGE JOIN (SEMI)

Description

Performs a merge semi join between two row sources

Versions

This operation is implemented in the following versions

Example

Columns do not need NOT NULL constraints.

This example was developed using Oracle 9.2.0.1 on Windows 2000

This example requires the following table definition

    CREATE TABLE t1 (c1 NUMBER,c2 NUMBER);
    CREATE TABLE t2 (c1 NUMBER,c2 NUMBER);

The table does not need to be analysed

The statement

    SELECT c2
    FROM t1
    WHERE EXISTS
    (
      SELECT /*+ MERGE_SJ */ c1 FROM t2
      WHERE t1.c1 = t2.c1
    );

generates the following execution plan

0     SELECT STATEMENT Optimizer=CHOOSE
1   0   MERGE JOIN (SEMI)
2   1     SORT (JOIN)
3   2       TABLE ACCESS (FULL) OF 'T1'
4   1     SORT (UNIQUE)
5   4       TABLE ACCESS (FULL) OF 'T2'