EXISTS Condition in Oracle SQL – PLSQL

The EXISTS condition in Oracle SQL / PLSQL will return any records whenever the “exists” condition is met.
EXISTS condition can be used with SELECT, INSERT, UPDATE and DELETE SQL statements.

Syntax for the EXISTS condition in Oracle SQL / PLSQL is:

SELECT column_name(s)
FROM table_name
WHERE EXISTS (subquery);

Or

INSERT INTO table_name
VALUES(column_name1
,column_name2
,column_name3
.
.
column_nameN)
WHERE EXISTS (subquery);

Or

UPDATE table_name
SET (column_name1 = value/expression
,column_name2 = value/expression
, column_name3 = value/expression
.
.
)
WHERE EXISTS (subquery);

Or

DELETE FROM table_name
WHERE EXISTS (subquery);

Let’s take an example for understanding:
Suppose have a table named ‘employee’ in the database as shown below.

Employee_ID Employee_Name Salary Department Commission
101 Emp A 10000 Sales 10
102 Emp B 20000 IT 20
103 Emp C 28000 IT 20
104 Emp D 30000 Support
105 Emp E 32000 Sales 10

And suppose we also have a table named “comm” as shown below:

Emp_ID Commission_Percent
101 10
102 20
103 20

Scenario 1:

Suppose we want to see the records of employee(s) from ‘employee’ table that also have records in ‘comm’ table.

The above can be achieved as:

SELECT *
FROM employee
WHERE EXISTS(SELECT *
             FROM comm
             WHERE employee.employee_id = comm.emp_id
             );

The result of the above query will be:

Employee_ID Employee_Name Salary Department Commission
101 Emp A 10000 Sales 10
102 Emp B 20000 IT 20
103 Emp C 28000 IT 20

Here we have retrieved the records pertaining to employee(s) from ‘employee’ table that also have records in ‘comm’ table using EXISTS condition along with WHERE clause.


Scenario 2:

EXISTS condition can also be used with NOT operator.
Let’s assume that we have a new table namely ‘employee’ as shown below:

Employee_ID Employee_Name Salary Department Commission
101 Emp A 10000 Sales 10
102 Emp B 20000 IT 20
103 Emp C 28000 IT 20
104 Emp D 30000 Support
105 Emp E 32000 Sales 10

And suppose we also have a table named “comm” as shown below:

Emp_ID Commission_Percent
101 10
102 20
103 20

Suppose we want to see the records of employee(s) from ‘employee’ table that do not have records in ‘comm’ table.
We can achieve the same as:

SELECT *
FROM employee
WHERE NOT EXISTS(SELECT *
                 FROM comm
                 WHERE employee.employee_id = comm.emp_id
                 );

Once we have run the above code following will be the result:

Employee_ID Employee_Name Salary Department Commission
104 Emp D 30000 Support
105 Emp E 32000 Sales 10

Here we have successfully retrieved the records pertaining to employee(s) from ‘employee’ table that do not have records in ‘comm’ table using EXISTS condition with NOT operator in combination with WHERE clause.


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