Speed up a slow database query

Prompt that reads a slow SQL query with its execution plan, finds the most expensive steps and suggests improvements with benefit and risk. Paste it into an AI tool of your choice, which then speeds up the query.

Topic: Coding & agents
Type: Prompt
Level: Intermediate
Time: about 8 min

Results depend on the tool, the model and what you enter.

Result preview

Example: written by our editors, not real AI output.

The query returns a customer's open orders from the last 90 days. Most expensive step: full scan of orders (1.2 million rows) because there is no index on (customer_id, status). Suggestion 1: index on orders (customer_id, status, created_at). Expected: run time from about 900 ms to under 20 ms. Side effect: slightly slower writes, about 40 MB more storage. Measure: EXPLAIN ANALYZE before and after, run time in monitoring for one week. Assumption: status has only a few distinct values.

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DatabaseWhich database do you use?

FrequencyHow often does the query run?

QueryPaste the query, execution plan and index list, without real customer data

Your prompt

Help me speed up a slow database query.
Database: [Database]
How often the query runs: [Frequency]
Query, execution plan and existing indexes:
<query>
[Query]
</query>
Approach: 1. Describe in two sentences what the query returns. 2. Read the execution plan and name the three most expensive steps, such as full table scans, large sorts or nested loops over many rows. 3. Suggest one change per problem: a suitable index, a rewritten condition, fewer columns, pre-filtering or splitting. 4. For each suggestion, state the expected effect, the side effect on writes and storage, and how to measure the result. 5. Check that the query result stays the same and mark every assumption with "Assumption:". Do not invent tables or columns that are not in the material.

Take particular care to name a way to measure and the side effect for every suggestion and never invent tables or columns.

Before you answer, check: Are all instructions met? If key information is missing or a placeholder in square brackets is still in the text, ask instead of guessing. Mark assumptions as assumptions.

Help me speed up a slow database query.
Database: [Database]
How often the query runs: [Frequency]
Query, execution plan and existing indexes:
<query>
[Query]
</query>
Approach: 1. Describe in two sentences what the query returns. 2. Read the execution plan and name the three most expensive steps, such as full table scans, large sorts or nested loops over many rows. 3. Suggest one change per problem: a suitable index, a rewritten condition, fewer columns, pre-filtering or splitting. 4. For each suggestion, state the expected effect, the side effect on writes and storage, and how to measure the result. 5. Check that the query result stays the same and mark every assumption with "Assumption:". Do not invent tables or columns that are not in the material.

Take particular care to name a way to measure and the side effect for every suggestion and never invent tables or columns.

Before you answer, check: Are all instructions met? If key information is missing or a placeholder in square brackets is still in the text, ask instead of guessing. Mark assumptions as assumptions.

This is an instruction for an AI, not the result itself.

Where this prompt works

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How to use it

Fill in the fields or tap a suggestion. Leave out names, addresses and other personal data.
Copy the finished prompt into an AI tool of your choice.
Test every suggestion on a copy with a realistic amount of data first and compare run time and result before you deploy it.

Why does this work?

The execution plan shows where the time is really lost. Naming the cost for writes avoids indexes that slow things down elsewhere.

Tips

An execution plan with real timings, for example from EXPLAIN ANALYZE, says much more than the estimated version.

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Speed up a slow database query

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