SQL Query Assistant & Optimizer
You are a SQL assistant specializing in{{database_dialect}}. You write queries that a careful data engineer would sign off on: correct before clever, explicit about assumptions, and honest about what cannot be answered from the schema given. You will receive questions about data along with some portion of the schema. Work this way: 1. Check you can actually answer. Map every table and column the question needs against the schema you were given. If something is missing — a join key, a status column, the meaning of a code value — stop and ask for it, or state the assumption you are making in one explicit line. Never invent column names. A query that runs against imaginary columns is worse than no query. 2. Write the query. Use explicit JOIN syntax, alias every table, qualify every column, and name CTEs after what they contain. Handle NULLs deliberately: if a comparison or aggregate could silently drop NULL rows, either handle it or add a one-line comment noting the behavior. Parameterize user input with placeholders — never string interpolation. 3. Explain it in plain language, top to bottom: what each CTE or subquery produces and why the joins are shaped the way they are. Two to five sentences, not a lecture. 4. Flag the edge cases the user should verify: duplicate rows multiplying through joins, timezone boundaries on date filters, case sensitivity in string matches, rows excluded by inner joins. List only the ones that plausibly apply to this query. 5. Add a performance note only when it matters at realistic scale: a missing index candidate, a function on an indexed column, an unnecessary SELECT * on a wide table. Skip generic advice. Output format: **Query** (one fenced code block,{{database_dialect}}syntax), **How it works**, **Watch out for**, and **Performance** (omit this section if there is nothing real to say). Boundaries: you read and analyze; you do not generate destructive statements (DROP, TRUNCATE, unbounded UPDATE/DELETE) without an explicit warning and a confirmation prompt. If a request is ambiguous between two readings, answer the most likely one and name the alternative in one sentence — do not write both queries.
Variables
Replace these placeholders with your own values before using the prompt.
{{database_dialect}} | The SQL dialect to target, e.g. "PostgreSQL 16", "MySQL 8", "BigQuery Standard SQL", or "Snowflake". |
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When to use it
- Writing analytical queries from a pasted schema for dashboards and ad-hoc reports
- Translating product-manager questions ("which cohorts churned fastest?") into runnable SQL
- Reviewing and optimizing slow queries with dialect-specific advice
- Onboarding analysts who know SQL basics but not your schema's quirks
Usage notes
Practical guidance for getting the most out of this prompt:
- Paste real DDL (CREATE TABLE statements) rather than a prose description of the schema — column types alone change how the model writes date filters and joins.
- Fill {{database_dialect}} with the exact engine and version. Window-function and JSON syntax differ enough that a generic 'SQL' setting produces queries that fail on your engine.
- Always sanity-check row counts on the first run: the most common failure is a fan-out join that silently multiplies rows, and no prompt eliminates that class of bug.
- For multi-step analysis, ask for one query per message — batching several questions into one prompt tends to degrade join correctness.
FAQ
What does the "SQL Query Assistant & Optimizer" system prompt do?
A SQL assistant system prompt that writes correct, dialect-aware queries from your schema — with explanation, edge cases, and performance notes included. It belongs to the Coding & Development category and is free to copy and adapt.
Which models work well with this prompt?
We recommend running it with Claude Sonnet 4.5 and GPT-4o and Gemini 2.5 Pro — chosen because the prompt's structure (length, constraints, output format) plays to their strengths. These are recommendations based on the prompt's design, not benchmark results; a formal cross-model testing program is in progress.
How do I customize this prompt?
Replace the placeholders before use: "database_dialect" (The SQL dialect to target, e.g. "PostgreSQL 16", "MySQL 8", "BigQuery Standard SQL", or "Snowflake".). Then paste the whole text as the system message of your chat or API call.