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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

  1. CREATE TABLE  “DEPARTMENTS”
  2.    (    “DEPARTMENT_ID” NUMBER(10,0) NOT NULL ENABLE,
  3.     “DEPARTMENT_NAME” VARCHAR2(50) NOT NULL ENABLE,
  4.      CONSTRAINT “DEPARTMENTS_PK” PRIMARY KEY (“DEPARTMENT_ID”) ENABLE
  5.    )
  6. /

anti-join1

Customer table

  1. CREATE TABLE  “CUSTOMER”
  2.    (    “CUSTOMER_ID” NUMBER,
  3.     “FIRST_NAME” VARCHAR2(4000),
  4.     “LAST_NAME” VARCHAR2(4000),
  5.     “DEPARTMENT_ID” NUMBER
  6.    )
  7. /

anti-join2

Execute this query

  1. SELECT   departments.department_id, departments.department_name
  2.         FROM     departments
  3.         WHERE    NOT EXISTS
  4.                  (
  5.                  SELECT 1
  6.                  FROM   customer
  7.                  WHERE customer.department_id = departments.department_id
  8.                  )
  9.         ORDER BY departments.department_id;

Output

anti-join3

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