SQL Temporary Tables: A Quick and Practical Guide

Temporary tables in SQL help manage large queries efficiently. They are session-specific and get removed automatically when no longer needed. This guide explains how to create them and when to use them.

Creating SQL Temp Tables

SQL Server:

CREATE TABLE #TempTable (ID INT PRIMARY KEY, Name NVARCHAR(100));

• # creates a session-specific temp table.

PostgreSQL:

CREATE TEMP TABLE TempTable (ID SERIAL PRIMARY KEY, Name TEXT);

• Uses TEMP to define temporary tables.

Common Use Cases

🔹 Staging Data Before Inserting into Main Tables

Use temp tables to validate and filter data before committing to permanent tables.

INSERT INTO MainTable (Name, Age, Email) 
SELECT Name, Age, Email 
FROM #ImportedData WHERE Age > 18;
DROP TABLE #ImportedData;

🔹 Aggregating and Transforming Data

CREATE TEMP TABLE temp_results AS
SELECT column1, SUM(value)
FROM large_table GROUP BY column1;

This makes large queries more efficient.

🔹 Query Optimization

Temp tables help speed up searches by storing intermediate results.

CREATE TEMP TABLE temp_results AS
SELECT column1, COUNT(*)
FROM large_table GROUP BY column1;

FAQ

How do temp tables work?

They store temporary data and disappear after the session ends.

Do I need to delete temp tables manually?

Usually, no. They drop automatically, but manual deletion is a good practice.

Can temp tables improve performance?

Yes, they help optimize queries by reducing repeated computations.

Are temp tables available across sessions?

Only global temp tables (##TempTable) are available across sessions.

Conclusion

Temporary SQL tables are powerful for staging, transforming, and optimizing data. They improve efficiency but should be used strategically to avoid unnecessary overhead.

Mastering their use can streamline complex queries and database operations.

Read the full article How to Create a Temporary Table with SQL.