SQL Server CTE vs Temporary Tables: When to Use Each

Introduction

Explain why developers often confuse CTEs and temporary tables and when each should be used.

What is a CTE?

Explain syntax with example.

WITH EmployeeCTE AS
(
    SELECT EmployeeID, Name
    FROM Employees
)
SELECT *
FROM EmployeeCTE;

What is a Temporary Table?

Example:

CREATE TABLE #Employees
(
    EmployeeID INT,
    Name NVARCHAR(100)
);

INSERT INTO #Employees
SELECT EmployeeID, Name
FROM Employees;

SELECT *
FROM #Employees;

Key Differences

Create a comparison table.

Feature	CTE	Temporary Table
Stored	No	Yes
Scope	Single statement	Session
Indexes	No	Yes
Statistics	No	Yes
Multiple reuse	No	Yes

Performance Comparison

Explain:

Small datasets
Large datasets
Recursive queries
Multiple joins

When to Use CTE

Examples:

Recursive hierarchy
Readability
One-time query
Breaking complex SQL

When to Use Temporary Tables

Examples:

Large datasets
Multiple joins
Stored procedures
Multiple query reuse

Recursive CTE Example

Employee hierarchy example.

Temporary Table Example

Monthly sales report.

Common Mistakes

Using CTE repeatedly in large queries
Forgetting to drop temp tables (optional; local temp tables are dropped automatically at session end, but explicit cleanup can still be good practice)
Choosing temp tables for tiny datasets
Assuming CTEs improve performance

Best Practices

Use CTEs for readability
Use temp tables for reuse
Test execution plans
Index temp tables when needed

Conclusion

Summarize the trade-offs and emphasize choosing based on workload rather than preference.

FAQ

Is a CTE faster than a temp table?
Can a CTE be indexed?
Can I join a CTE?
When should I use temp tables?

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