📀 SQL TEMPORARY TABLES – Store Session-Specific Data

🧲 Introduction – What Are SQL Temporary Tables?

Temporary tables are special types of tables that exist only for the duration of a session or transaction. They are useful for storing intermediate results, processing temporary logic, and isolating data from permanent tables.

🎯 In this guide, you’ll learn:

• How to create, use, and delete temporary tables
• Differences between local and global temp tables
• Best practices and platform-specific syntax

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✅ 1. CREATE TEMPORARY TABLE Syntax

-- MySQL / PostgreSQL
CREATE TEMPORARY TABLE temp_table_name (
  id INT,
  name VARCHAR(50)
);

-- SQL Server (local temp)
CREATE TABLE #temp_table (
  id INT,
  name VARCHAR(50)
);

✅ The table exists only for the session or procedure.

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🧪 2. Insert and Query from Temp Tables

INSERT INTO temp_table_name VALUES (1, 'Alice');
SELECT * FROM temp_table_name;

✅ Use just like regular tables, but scoped to session.

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🔄 3. Temp Table Lifecycle

Type	Visibility	Auto-Dropped When
TEMPORARY TABLE	Current session	Session ends
#Local (SQL Server)	Current session	Session ends
##Global (SQL Server)	All sessions	Last session ends

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🧹 4. Drop Temporary Table

DROP TEMPORARY TABLE temp_table_name;  -- MySQL / PostgreSQL
DROP TABLE #temp_table;                -- SQL Server

✅ Optional, but good hygiene before session exit.

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🧠 5. Temp Table Use Cases

• Break complex queries into steps
• Store session-level filters
• Stage intermediate results in ETL or reports
• Isolate test logic without altering permanent tables

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📘 Best Practices

✅ Recommended	❌ Avoid This
Use descriptive names with temp_ prefix	Polluting tempdb with unused tables
Drop table explicitly if long session	Relying solely on auto-drop
Use only for intermediate or private data	Storing critical business data

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📌 Summary – Recap & Next Steps

Temporary tables are a flexible way to hold intermediate or volatile data safely within a session or procedure. They’re great for reporting, testing, and procedural logic.

🔍 Key Takeaways:

• Use CREATE TEMPORARY TABLE for session-level isolation
• Supported by MySQL, PostgreSQL, SQL Server (with different syntax)
• Auto-dropped when session ends (unless explicitly dropped earlier)

⚙️ Real-World Relevance:
Used in testing, stored procedures, ETL pipelines, and advanced analytics.

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❓ FAQ – SQL Temporary Tables

❓ What is a temporary table?

✅ A table that lives only during the database session or transaction.

❓ Do I need to drop temp tables manually?

✅ Not strictly, but it’s a good habit for long-running sessions.

❓ Can I use indexes on temp tables?

✅ Yes. You can create indexes, constraints, and even joins.

❓ How is a temp table different from a table variable or CTE?

✅ Temp tables are real tables in memory/disk; variables and CTEs are lighter-weight alternatives.

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