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INTERSECT operator in Oracle

ORACLE INTERSECT
To compare the rows of two or more Oracle SELECT statements, the Oracle INTERSECT operator is used. After the comparing process, the INTERSECT operator returns the common or intersecting records from the corresponding columns of the selected expressions.

There are however two mandatory conditions for using the INTERSECT operator in Oracle.

  • Each SELECT statement must have the same number of expressions.
  • Each corresponding expression in the different SELECT statement should be of the same data type.

Syntax:

SELECT expr_1, expr_2, ... expr_n  
FROM table1  
WHERE conditions  
INTERSECT  
SELECT expr_1, expr_2, ... expr_n  
FROM table2  
WHERE conditions;   

Parameters:
expr_1, expr_2, … expr_n: It is used to specify the columns of the table which needs to be retrieved.
table1, table2: It is used to specify the name of the tables from which the records need to be retrieved.
conditions: It is used to specify the conditions to be strictly followed for selection.

Example 1: Fetching single field from two tables.
Students Table:

STUDENT_ID	NAME	AGE
1	Joy	20
2	Smiley	19
3	Happy	21
4	James	22
5	Bond	25

Teachers Table:

TEACHER_ID	NAME	AGE
101	        James	30
102	        Bond	25
103	        Smith	40

Query:

SELECT name  
FROM students
INTERSECT  
SELECT name 
FROM teachers;

Output:

NAME
James
Bond

Explanation:
The ‘students’ and the ‘teachers’ are the already existing tables. After the intersection, the common rows for the ‘name’ field from the ‘students’ table and the ‘teachers’ table would appear.

Example 2: Fetching multiple fields from two tables.
Students Table:

STUDENT_ID	NAME	AGE
1	        Joy	20
2	        Smiley	19
3	        Happy	21
4	        James	22
5	        Bond	25

Teachers Table:

TEACHER_ID	NAME	AGE
101	        James	30
102	        Bond	25
103	        Smith	40

Query:

SELECT name, age
FROM students
INTERSECT  
SELECT name, age
FROM teachers;

Output:

NAME	AGE
Bond	25

Explanation:
The ‘students’ and the ‘teachers’ are the already existing tables. After the intersection, the common rows for the ‘name’ and the ‘age’ fields from the ‘students’ table and the ‘teachers’ table would appear.

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