Oracle Anti Join

Anti-join is used to make the queries run faster. It is a very powerful SQL construct Oracle offers for faster queries.

Anti-join between two tables returns rows from the first table where no matches are found in the second table. It is opposite of a semi-join. An anti-join returns one copy of each row in the first table for which no match is found.

Anti-joins are written using the NOT EXISTS or NOT IN constructs.

Example

Let's take two tables "departments" and "customer"

Departments table

CREATE TABLE  "DEPARTMENTS" 
   (	"DEPARTMENT_ID" NUMBER(10,0) NOT NULL ENABLE, 
	"DEPARTMENT_NAME" VARCHAR2(50) NOT NULL ENABLE, 
	 CONSTRAINT "DEPARTMENTS_PK" PRIMARY KEY ("DEPARTMENT_ID") ENABLE
   )
/

Customer table

CREATE TABLE  "CUSTOMER" 
   (	"CUSTOMER_ID" NUMBER, 
	"FIRST_NAME" VARCHAR2(4000), 
	"LAST_NAME" VARCHAR2(4000), 
	"DEPARTMENT_ID" NUMBER
   )
/

Execute this query

SELECT   departments.department_id, departments.department_name
        FROM     departments
        WHERE    NOT EXISTS
                 (
                 SELECT 1
                 FROM   customer
                 WHERE customer.department_id = departments.department_id
                 )
        ORDER BY departments.department_id;

Output

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