SQL Query Explainer — Understand Any SQL Query

What Does the Explainer Show?

The explainer generates three outputs from your SQL:

1. Plain English Summary — A natural-language sentence describing what the query does. For example: "This query selects customer names and order totals from the customers and orders tables, joins them on customer_id, filters to paid orders, groups results by customer, and returns the top 10 by revenue."

2. Structured Breakdown — A card-based view showing the query type, tables used, columns selected, join conditions, filters, aggregations, sorting, and limiting. Each element is displayed in its own card for quick scanning.

3. Complexity Score — A numeric score from 0 to 100 with a label (Simple, Moderate, Complex, or Advanced) and a list of reasons explaining the score. A single-table SELECT with no joins scores low. A multi-CTE query with window functions, subqueries, and HAVING clauses scores high.

How the Complexity Score Works

The scoring algorithm adds points for structural complexity:

• +12 per JOIN — Each join increases the number of tables the reader must hold in memory
• +15 per subquery — Nested queries require understanding the inner query before the outer
• +12 per window function — OVER() clauses add a partitioning and ordering layer
• +10 per UNION — Combining result sets multiplies the mental model
• +8 for GROUP BY — Aggregation changes the granularity of the result
• +8 for CTEs — Common table expressions add named intermediate results
• +5 for HAVING — Post-aggregation filtering adds another condition layer
• +3 per aggregate function — COUNT, SUM, AVG, MIN, MAX each add a calculation
• +3 for DISTINCT — Deduplication implies potential data quality considerations

The score caps at 100. Scores are labeled: Simple (0–25), Moderate (26–45), Complex (46–70), Advanced (71–100).

No AI — Pure Structural Analysis

This tool does not use any AI, machine learning, or external API. Every explanation is derived by parsing the SQL text and analyzing its clauses, keywords, and structure using JavaScript running in your browser. This means the explanations are deterministic: the same query always produces the same explanation, and no data is ever sent to any server.

Use Cases

• Understand a complex query you inherited from a previous developer
• Document existing SQL queries with plain English descriptions
• Review query complexity before sending to production
• Learn SQL by seeing how clauses map to plain language
• Audit stored procedures to understand what each query does
• Compare the complexity of different approaches to the same problem