Stop Using CTEs for Everything: SQL Temp Tables vs. CTEs for Performance

SQL Performance: Stop Obsessing Over Elegant Syntax

Is your "clean code" actually slowing down your database? It's time to choose performance over prettiness.

The Problem: The Memory Trap

Common Table Expressions (CTEs) look great in your SQL editor. They make code readable and logical. However, on massive datasets, they can become a memory nightmare. Because CTEs aren't indexed, the database engine often has to re-evaluate them or struggle with huge intermediate result sets in memory.

The Warning: When joining millions of rows, an "elegant" CTE will often choke and time out, causing a system-wide performance bottleneck.

The Solution: The Iron Fortress of Temp Tables

Temp tables might not be as "pretty" as CTEs, but they are incredibly practical. They live in tempdb and allow for actual indexing and statistics generation. This gives the SQL optimizer the information it needs to execute your query efficiently.

Pro Tip: Use CTEs for readability on small-to-medium datasets. Switch to Temp Tables when performance scales to millions of rows.

Execution Comparison

-- THE PERFORMANCE WINNER
CREATE TABLE #LargeData (...);
CREATE INDEX IX_Data ON #LargeData(ID);

-- Query speed can improve by up to 80%
-- vs the standard WITH CTE AS (...) approach

It’s the difference between a glass bridge and an iron fortress. One is for aesthetics; the other is built for production-grade scale.

See it in action

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