Advanced Database Management System - Tutorials and Notes: INTERSECT Set Operator

Tuesday, 10 June 2014

INTERSECT Set Operator


SQL Set Operator INTERSECT and INTERSECT ALL / Supported Set Operators in various DBMSs / INTERSECT and INTERSECT ALL Set Operators with Examples


Let us use the following tables for explaining the concept of the INTERSECT set operator;
Regno
Name
Phone
10BS0123
Madhavan
9965235412
10BC0234
Jerry
8569326541
11BM0023
Malar
9658236542
11BC0003
Kumar
9653268954
Table 1 - UG_Student
Regno
Name
Phone
10MS0434
Noel
9856452314
10MS0012
Kumar
9653268954
11MC0070
Ramkumar
9965235412
Table 2 - PG_Student
INTERSECT operator is used to join two or more tables vertically, and displays only the records which are common for all the tables. That is, the INTERSECT operator filters the records which can be commonly found in all the tables according to the given expressions. For example, consider the query given below;
(SELECT Name, Phone FROM UG_Student) INTERSECT (SELECT Name, Phone FROM PG_Student);
----- Query 1
The result of this query will be;



Name
Phone
Kumar
9653268954
Table 3 - Result of  "(SELECT Name, Phone FROM UG_Student) INTERSECT (SELECT Name, Phone FROM PG_Student);"



The result shows the only common record according to the given expressions 1 (SELECT Name, Phone FROM UG_Student) and 2 (SELECT Name, Phone FROM PG_Student) of Query 1.



The INTERSECT operator can be used in two ways;
1. INTERSECT [Distinct] – Here Distinct keyword need not be specified.
2. INTERSECT ALL – Removes the duplicate tuples (records) from the result set. For intersect all, we will get the result as Table 4.


Name
Phone
Kumar
9653268954
Kumar
9653268954

Table 4 - Result of  "(SELECT Name, Phone FROM UG_Student) INTERSECT ALL (SELECT Name, Phone FROM PG_Student);"



Support for SQL Set Operator INTERSECT in Various DBMSs:

INTERSECT operator in MySQL

MySQL does not support INTERSECT. It can be achieved through other ways using the keywords IN or EXISTS. Query 1 is rewritten using the keyword IN as follows to achieve intersection in MySQL.

SELECT Name, Phone FROM UG_Student WHERE (Name, Phone) IN (SELECT Name, Phone FROM PG_Student);

 

INTERSECT operator in Oracle

Oracle supports INTERSECT operator as discussed above. The above example (Query 1) can be treated as example for Oracle INTERSECT operator.

INTERSECT operator in DB2

DB2 supports INTERSECT operator. Above examples can be treated as examples for DB2 too.

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