In Oracle, SEMI JOIN returns one copy of each row in first table for which at least one match is found. SEMI JOIN are written using the EXISTS construct. It provides an efficient method of performing a WHERE EXISTS sub-query.
To returns one copy of each row in first table for which at least one match is found, use the following syntax:
Parameters:
tablename1: The table name from which you want to fetch records.
col1: The column or field name that will be return.
Note:
In the above example, it returns one copy of each row in first table for which at least one match is found using SEMI JOIN.