Introduction to PostgreSQL Temporary Tables

Understanding Temporary Tables

Temporary tables in PostgreSQL are special kinds of tables that exist only for the duration of a database session. They are useful for storing intermediate results temporarily without affecting the main database schema.

Creating a Temporary Table

Syntax for Creating Temporary Tables

To create a temporary table, use the CREATE TEMPORARY TABLE statement followed by the table name and column definitions.


CREATE TEMPORARY TABLE temp_employees (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    department VARCHAR(50)
);

Inserting Data into Temporary Tables

Adding Records to Temporary Tables

Data can be inserted into temporary tables using the standard INSERT INTO statement.


INSERT INTO temp_employees (name, department) VALUES ('Alice', 'HR');
INSERT INTO temp_employees (name, department) VALUES ('Bob', 'Engineering');

Querying Temporary Tables

Selecting Data from Temporary Tables

You can query temporary tables just like regular tables using the SELECT statement.


SELECT * FROM temp_employees;

Updating Data in Temporary Tables

Modifying Records in Temporary Tables

Use the UPDATE statement to modify existing records in a temporary table.


UPDATE temp_employees SET department = 'Marketing' WHERE name = 'Alice';

Deleting Data from Temporary Tables

Removing Records from Temporary Tables

Records can be removed from temporary tables using the DELETE statement.


DELETE FROM temp_employees WHERE name = 'Bob';

Dropping Temporary Tables

Removing Temporary Tables

Temporary tables can be dropped using the DROP TABLE statement. They are also automatically dropped at the end of the session.


DROP TABLE IF EXISTS temp_employees;

Using Temporary Tables with Joins

Combining Temporary and Regular Tables

Temporary tables can be joined with regular tables to perform complex queries and data manipulation.


SELECT e.name, e.department, d.manager 
FROM temp_employees e
JOIN departments d ON e.department = d.name;

Temporary Tables in Transactions

Ensuring Data Integrity

Temporary tables can be used within transactions to ensure data integrity and rollback changes if needed.


BEGIN;
CREATE TEMPORARY TABLE temp_sales AS SELECT * FROM sales WHERE date = '2023-10-01';
-- Perform operations on temp_sales
ROLLBACK;

Performance Considerations

Optimizing Temporary Table Usage

While temporary tables are useful, they can consume resources. It's important to manage them efficiently to avoid performance issues.


-- Example of efficient use
CREATE TEMPORARY TABLE temp_large_data AS SELECT * FROM large_data WHERE condition;
-- Process data
DROP TABLE IF EXISTS temp_large_data;