Creating temporary tables in SQL

Cloning table structures swiftly

To copy a table's structure without its data, use CREATE TEMPORARY TABLE ... LIKE:

-- Like creating a doppelganger, minus the existential crisis
CREATE TEMPORARY TABLE temp_table LIKE existing_table;


This ensures column types, indexes, and defaults cloning, without the burden of data duplication.

Reducing overhead via CTEs

Utilize Common Table Expressions (CTEs) as temporary "in-memory tables", existing only during the query execution:

-- Structuring chaos, one CTE at a time
WITH cte AS (
    SELECT * FROM source_table WHERE condition
)
SELECT cte.* FROM cte JOIN other_table ON cte.id = other_table.id;


CTEs and subqueries ably avoid creating physical temporary tables, leading to more efficient resources management.

Keep Schema search path in check

While operating with temporary tables, ensure your schema search path includes pg_temp—PostgreSQL's home for session-specific temporary tables:

-- Keep an eye on your path, don't get lost
SHOW search_path;
-- Adding 'pg_temp' to your GPS
SET search_path TO pg_temp, public;


Disposing off temporary tables

Temporary tables, courtesy of their fleeting nature, get automatically cleaned up post database session or transaction. However, achieving transparency may require a manual purge:

-- Because sometimes, manual labor is just more satisfying
DROP TEMPORARY TABLE IF EXISTS temp_table;


Be wary while dealing with transaction-scoped temporary tables—persistent for the present transaction only. Post-transaction access attempts may yield unexpected outcomes.

Replicating structures via LIKE

LIKE proves handy when creating a temp table sporting the same structure as an existing entity:

-- Keeping you in the loop... 'LIKE'
CREATE TEMPORARY TABLE temp_table LIKE existing_table INCLUDING ALL;


This including all ensures replication of defaults, constraints, and indexes from the original table.

On-the-fly querying with CREATE VIEW

At times, temp tables can seem restrictive. For those moments, turn to a view offering a dynamic data window:

-- When static proves to be a bit too static...
CREATE OR REPLACE VIEW my_view AS
SELECT * FROM my_table WHERE register_type = 'gen';


This tactic is ideal for those avoiding data materialization and seeking query optimizations.

Multi-tasking with multiple CTEs

Divide and conquer complex operations by breaking them down into multiple CTEs:

-- Complexity ain't got nothin' on you
WITH sorted AS (
    SELECT * FROM temp_table ORDER BY id
),
filtered AS (
    SELECT * FROM sorted WHERE name LIKE 'A%'
)
SELECT * FROM filtered;


Individual CTEs refine the dataset phase-wise, culminating in simpler and cleaner code.

Correct syntax: The key to success

Staying on top of the syntax and best practices is crucial while creating temporary tables. SELECT INTO though capable of creating temporary tables, is best avoided in favor of CREATE TEMPORARY TABLE as it may lead to ambiguous behavior.

Static data snapshots for consistency

A static snapshot of data within a temporary table can help maintain consistent reference throughout a session:

-- Creating a time capsule for your data
CREATE TEMPORARY TABLE temp_snapshot AS
SELECT * FROM real_time_data;


This snapshot remains immutable till the end of the session, regardless of the base table transformations.

Cleanup and resource management

Although temporary tables drop automatically at session/transaction conclusion, best practice recommends actively dropping tables post usage:

-- Wipe your footprints before leaving
DROP TEMPORARY TABLE IF EXISTS temp_table;


Proactive management of temporary tables ensures database resources optimization and minimal schema clutter.