PostgreSQL TRUNCATE TABLE Statement

PostgreSQL TRUNCATE TABLE Statement

The PostgreSQL TRUNCATE TABLE statement is used to quickly remove all rows from a table, effectively resetting the table while preserving its structure. This statement is essential for efficiently clearing out large tables without the overhead of individual row deletions.

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Syntax

TRUNCATE TABLE table_name [CASCADE | RESTRICT];

The TRUNCATE TABLE statement has the following components:

• table_name: The name of the table to be truncated.
• CASCADE: Optional. Automatically truncates all tables that have foreign-key references to the truncated table.
• RESTRICT: Optional. Refuses to truncate the table if there are any foreign-key references to it. This is the default behavior.

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Example PostgreSQL TRUNCATE TABLE Statement Queries

Let's look at some examples of PostgreSQL TRUNCATE TABLE statement queries:

1. Basic TRUNCATE TABLE Example

TRUNCATE TABLE employees;

This query removes all rows from the employees table.

2. TRUNCATE TABLE with CASCADE

TRUNCATE TABLE employees CASCADE;

This query removes all rows from the employees table and automatically truncates all tables that have foreign-key references to it.

3. TRUNCATE TABLE with RESTRICT

TRUNCATE TABLE employees RESTRICT;

This query removes all rows from the employees table only if there are no foreign-key references to it. This is the default behavior.

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Full Example

Let's go through a complete example that includes creating a table, inserting data, and then truncating the table.

Step 1: Creating a Table

This step involves creating a new table named employees to store employee data.

CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    first_name VARCHAR(50),
    last_name VARCHAR(50),
    email VARCHAR(100)
);

In this example, we create a table named employees with columns for id, first_name, last_name, and email.

Step 2: Inserting Data into the Table

This step involves inserting some sample data into the employees table.

INSERT INTO employees (first_name, last_name, email)
VALUES ('John', 'Doe', 'john.doe@example.com');

INSERT INTO employees (first_name, last_name, email)
VALUES ('Jane', 'Smith', 'jane.smith@example.com');

Here, we insert data into the employees table, including values for the first_name, last_name, and email columns.

Step 3: Truncating the Table

This step involves removing all rows from the employees table.

TRUNCATE TABLE employees;

Here, we truncate the employees table, effectively removing all rows while preserving the table structure.

Conclusion

The PostgreSQL TRUNCATE TABLE statement is a fundamental tool for efficiently clearing out large tables. Understanding how to use the TRUNCATE TABLE statement and its syntax is essential for effective database management and maintenance in PostgreSQL.