Creating Temporary Tables in SQL — Methods, Trade-offs, and Best Practices

1. Why Temporary Tables Matter

Temporary tables help analysts:

• Break complex logic into stages
• Store intermediate results
• Avoid repeating filtering logic
• Improve readability
• Reduce risk of typos in repeated subqueries

They function as short-term working tables during analysis.

There are multiple ways to create them depending on the RDBMS (Relational Database Management System) being used.

2. Common Ways to Create Temporary Tables

We will compare three approaches:

1. WITH clause (Common Table Expression, CTE)
2. SELECT INTO
3. CREATE TABLE (or CREATE TEMP TABLE)

Each method serves different purposes.

3. Method 1: WITH Clause (CTE)

Purpose

Creates a temporary result set used within a single query.

Syntax

WITH table_name AS (
    SELECT ...
    FROM ...
    WHERE ...
)
SELECT ...
FROM table_name;

WITH table_name AS (
    SELECT ...
    FROM ...
    WHERE ...
)
SELECT ...
FROM table_name;

Characteristics

• Exists only for the duration of the query.
• Not stored permanently.
• Improves readability.
• Ideal for multi-step logic.
• Supported in BigQuery and most modern SQL systems.

Pros

• Clean structure.
• Easy to reuse within one query.
• Does not modify database structure.

Cons

• Cannot persist across sessions.
• Cannot be reused in separate queries without rewriting.

4. Method 2: SELECT INTO

Purpose

Creates a new table from a query result.

Example (Not supported in BigQuery, but common in other systems)

SELECT *
INTO Africa_Sales
FROM global_sales
WHERE region = 'Africa';

SELECT *
INTO Africa_Sales
FROM global_sales
WHERE region = 'Africa';

Characteristics

• Copies data into a new table.
• Typically session-scoped (depends on RDBMS).
• Does not permanently alter core database structure.

Pros

• Simple syntax.
• Quick way to create working copy.
• Keeps primary database uncluttered.

Cons

• Not supported in all systems (e.g., BigQuery).
• Behavior varies across RDBMSs.

5. Method 3: CREATE TABLE

Purpose

Creates a permanent table in the database.

Syntax

CREATE TABLE Africa_Sales AS
SELECT *
FROM global_sales
WHERE region = 'Africa';

CREATE TABLE Africa_Sales AS
SELECT *
FROM global_sales
WHERE region = 'Africa';

Characteristics

• Adds table permanently to database.
• Can include metadata definitions.
• Usable across sessions.
• Accessible to others (depending on permissions).

Pros

• Persistent.
• Shareable.
• Useful for complex or reusable transformations.
• Allows metadata documentation.

Cons

• Clutters database if overused.
• Requires cleanup when no longer needed.
• May require permissions.

6. CREATE TEMP TABLE

Some RDBMSs support:

CREATE TEMP TABLE table_name AS
SELECT ...

CREATE TEMP TABLE table_name AS
SELECT ...

Characteristics

• Session-scoped.
• Not permanently stored.
• Cleaner than permanent tables.
• Explicitly temporary.

Syntax varies across systems.

7. Choosing the Right Approach

8. When Temporary Tables Improve Workflow

Use temp tables when:

• Joining multiple large tables.
• Performing repeated calculations on a subset.
• Collecting outputs from multiple databases.
• Simplifying deeply nested subqueries.
• Improving debugging clarity.

9. When Temporary Tables May Interrupt Workflow

Potential drawbacks:

• Extra execution step.
• Slight overhead.
• Need to rerun creation step in new session.
• Possible permission constraints.

However, the benefits usually outweigh the drawbacks in complex analysis.

10. Code Readability and Collaboration

Temporary tables:

• Make SQL easier to read.
• Reduce repeated code blocks.
• Lower risk of copy-paste errors.
• Help teammates understand logic flow.

Readable code improves collaboration.

11. Practical Comparison Example

Instead of repeating:

SELECT ...
FROM trips
WHERE trip_duration >= 60;

SELECT ...
FROM trips
WHERE trip_duration >= 60;

Multiple times, define once:

WITH long_trips AS (
    SELECT *
    FROM trips
    WHERE trip_duration >= 60
)

WITH long_trips AS (
    SELECT *
    FROM trips
    WHERE trip_duration >= 60
)

Then reuse long_trips.

This reduces redundancy.

12. RDBMS Differences

Different systems may require:

• SELECT INTO
• CREATE TABLE
• CREATE TEMP TABLE
• Session-specific syntax

Always check documentation for:

• BigQuery
• MySQL
• PostgreSQL
• SQL Server
• Oracle

Syntax differences are normal across systems.

13. Best Practices

1. Use descriptive names.
2. Keep scope clear (temporary vs permanent).
3. Avoid creating unnecessary permanent tables.
4. Clean up unused tables.
5. Document complex logic.
6. Balance efficiency and readability.

14. Summary

Temporary tables can be created using:

• WITH (CTE) — query-scoped temporary logic.
• SELECT INTO — copy-based creation (RDBMS dependent).
• CREATE TABLE — permanent storage.
• CREATE TEMP TABLE — session-based temporary storage.

They help:

• Organize complex SQL.
• Reduce repetition.
• Improve readability.
• Enhance workflow efficiency.

Temporary tables are powerful structural tools that support scalable, maintainable SQL analysis.