PostgreSQL Tutorial: DROP TABLE

Summary: In this tutorial, you will learn how to use the PostgreSQL DROP TABLE statement to remove existing tables from the database.

Table of Contents

Introduction to PostgreSQL DROP TABLE statement

To drop a table from the database, you use the DROP TABLE statement as follows:

DROP TABLE [IF EXISTS] table_name 
[CASCADE | RESTRICT];

In this syntax:

• First, specify the name of the table that you want to drop after the DROP TABLE keywords.
• Second, use the IF EXISTS option to remove the table only if it exists.

If you remove a table that does not exist, PostgreSQL issues an error. To avoid this situation, you can use the IF EXISTS option.

In case the table that you want to remove is used in other objects such as views, triggers, functions, and stored procedures, the DROP TABLE cannot remove the table. In this case, you have two options:

• The CASCADE option allows you to remove the table and its dependent objects.
• The RESTRICT option rejects the removal if there is any object depends on the table. The RESTRICT option is the default if you don’t explicitly specify it in the DROP TABLE statement.

To remove multiple tables at once, you can place a comma-separated list of tables after the DROP TABLE keywords:

DROP TABLE [IF EXISTS] 
   table_name_1,
   table_name_2,
   ...
[CASCADE | RESTRICT];

Note that you need to have the roles of the superuser, schema owner, or table owner in order to drop tables.

PostgreSQL DROP TABLE examples

Let’s take some examples of using the PostgreSQL DROP TABLE statement

1) Drop a table that does not exist

The following statement removes a table named authorin the database:

DROP TABLE author;

PostgreSQL issues an error because the author table does not exist.

ERROR:  table "author" does not exist

To avoid the error, you can use the IF EXISTS option like this.

DROP TABLE IF EXISTS author;

NOTICE:  table "author" does not exist, skipping DROP TABLE

As can be seen clearly from the output, PostgreSQL issued a notice instead of an error.

2) Drop a table that has dependent objects

The following creates new tables called authors and pages:

CREATE TABLE authors (
	author_id INT PRIMARY KEY,
	firstname VARCHAR (50),
	lastname VARCHAR (50)
);

CREATE TABLE pages (
	page_id serial PRIMARY KEY,
	title VARCHAR (255) NOT NULL,
	contents TEXT,
	author_id INT NOT NULL,
	FOREIGN KEY (author_id) 
          REFERENCES authors (author_id)
);

The following statement uses the DROP TABLE to drop the authortable:

DROP TABLE IF EXISTS authors;

Because the constraint on the page table depends on the authortable, PostgreSQL issues an error message:

ERROR:  cannot drop table authors because other objects depend on it
DETAIL:  constraint pages_author_id_fkey on table pages depends on table authors
HINT:  Use DROP ... CASCADE to drop the dependent objects too.
SQL state: 2BP01

In this case, you need to remove all dependent objects first before dropping the author table or use CASCADE option as follows:

DROP TABLE authors CASCADE;

PostgreSQL removes the authortable as well as the constraint in the page table.

If the DROP TABLE statement removes the dependent objects of the table that is being dropped, it will issue a notice like this:

NOTICE:  drop cascades to constraint pages_author_id_fkey on table pages

3) Drop multiple tables

The following statements create two tables for the demo purposes:

CREATE TABLE tvshows(
	tvshow_id INT GENERATED ALWAYS AS IDENTITY,
	title VARCHAR,
	release_year SMALLINT,
	PRIMARY KEY(tvshow_id)
);

CREATE TABLE animes(
	anime_id INT GENERATED ALWAYS AS IDENTITY,
	title VARCHAR,
	release_year SMALLINT,
	PRIMARY KEY(anime_id)
);

The following example uses a single DROP TABLE statement to drop the tvshows and animes tables:

DROP TABLE tvshows, animes;

Summary

• Use the DROP TABLE statement to drop a table.
• Use the CASCADE option to drop a table and all of it dependent objects.

See more

PostgreSQL Tutorial