Oracle DROP TABLE

Summary: in this tutorial, you will learn how to use the Oracle DROP TABLE statement to remove an existing table.

Introduction to Oracle DROP TABLE statement

To move a table to the recycle bin or remove it entirely from the database, you use the DROP TABLE statement:

DROP TABLE schema_name.table_name
[CASCADE CONSTRAINTS | PURGE];

In this statement:

• First, indicate the table and its schema that you want to drop after the DROP TABLE clause. If you don’t specify the schema name explicitly, the statement assumes that you are removing the table from your own schema.
• Second, specify CASCADE CONSTRAINTS clause to remove all referential integrity constraints which refer to primary and unique keys in the table. In case such referential integrity constraints exist and you don’t use this clause, Oracle returns an error and stops removing the table.
• Third, specify PURGE clause if you want to drop the table and release the space associated with it at once. By using the PURGE clause, Oracle will not place the table and its dependent objects into the recycle bin.

Notice that the PURGE clause does not allow you to roll back or recover the table that you dropped. Therefore, it is useful if you don’t want the sensitive data to appear in the recycle bin.

Oracle DROP TABLE examples

Let’s look at some examples of using the DROP TABLE statement.

Basic Oracle DROP TABLE example

The following CREATE TABLE statement creates persons table for the demonstration:

CREATE TABLE persons (
    person_id NUMBER,
    first_name VARCHAR2(50) NOT NULL,
    last_name VARCHAR2(50) NOT NULL,
    PRIMARY KEY(person_id)
);  

The following example drops the persons table from the database:

DROP TABLE persons;

Oracle DROP TABLE CASCADE CONSTRAINTS example

The following statements create two new tables named brands and cars:

CREATE TABLE brands(
    brand_id NUMBER PRIMARY KEY,
    brand_name varchar2(50)
);

CREATE TABLE cars(
    car_id NUMBER PRIMARY KEY,
    make VARCHAR(50) NOT NULL,
    model VARCHAR(50) NOT NULL,
    year NUMBER NOT NULL,
    plate_number VARCHAR(25),
    brand_id NUMBER NOT NULL,

    CONSTRAINT fk_brand 
    FOREIGN KEY (brand_id) 
    REFERENCES brands(brand_id) ON DELETE CASCADE
);

In these tables, each brand has 1 or more cars while each car belongs to only one brand.

The following statement tries to drop the brands table:

DROP TABLE brands;

Oracle issued the following error:

ORA-02449: unique/primary keys in table referenced by foreign keys

This is because the primary key of the brands table is currently referenced by the brand_id column in the cars table.

The following statement returns all foreign key constraints of the cars table:

SELECT
    a.table_name,
    a.column_name,
    a.constraint_name,
    c.owner,
    c.r_owner,
    c_pk.table_name r_table_name,
    c_pk.constraint_name r_pk
FROM
    all_cons_columns a
JOIN all_constraints c ON
    a.owner = c.owner
    AND a.constraint_name = c.constraint_name
JOIN all_constraints c_pk ON
    c.r_owner = c_pk.owner
    AND c.r_constraint_name = c_pk.constraint_name
WHERE
    c.constraint_type = 'R'
    AND a.table_name = 'CARS';

To drop the brands table, you must use the CASCADE CONSTRAINTS clause as follows:

DROP TABLE brands CASCADE CONSTRAINTS;

This statement dropped not only the brands table but also the foreign key constraint fk_brand from the cars table.

If you execute again the statement to get the foreign key constraints in the cars table, you will not see any row returned.

Oracle DROP TABLE PURGE example

The following statement drops the cars table using the PURGE clause:

DROP TABLE cars purge;

Drop multiple tables at once

Oracle provides no direct way to drop multiple tables at once. However, you can use the following PL/SQL block to do it:

BEGIN
  FOR rec IN
    (
      SELECT
        table_name
      FROM
        all_tables
      WHERE
        table_name LIKE 'TEST_%'
    )
  LOOP
    EXECUTE immediate 'DROP TABLE  '||rec.table_name || ' CASCADE CONSTRAINTS';
  END LOOP;
END;
/

This block deletes all tables whose names start with TEST_.

To test this code, you can first create three tables: test_1, test_2 and test_3 as follows:

CREATE TABLE test_1(c1 VARCHAR2(50));
CREATE TABLE test_2(c1 VARCHAR2(50));
CREATE TABLE test_3(c1 VARCHAR2(50));

Then, execute the PL/SQL block above.

In this tutorial, you have learned how to use the Oracle DROP TABLE statement to drop a table from the database.