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query-writing

★ 25,749

by langchain-ai · part of langchain-ai/deepagents

Writes and executes SQL queries from simple SELECTs to complex multi-table JOINs, aggregations, and subqueries. Use when the user asks to query a database, write SQL, run a SELECT statement, retrieve data, filter records, or generate reports from database tables.

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#database#git
🧩 One of 7 skills in the langchain-ai/deepagents package — works on its own, and pairs well with its siblings.

This is the playbook your agent receives when the skill activates — you don't need to read it to use the skill, but it's here to audit before installing.

Query Writing Skill

Workflow for Simple Queries

For straightforward questions about a single table:

  1. Identify the table - Which table has the data?
  2. Get the schema - Use sql_db_schema to see columns
  3. Write the query - SELECT relevant columns with WHERE/LIMIT/ORDER BY
  4. Execute - Run with sql_db_query
  5. Format answer - Present results clearly

Workflow for Complex Queries

For questions requiring multiple tables:

1. Plan Your Approach

Use write_todos to break down the task:

  • Identify all tables needed
  • Map relationships (foreign keys)
  • Plan JOIN structure
  • Determine aggregations

2. Examine Schemas

Use sql_db_schema for EACH table to find join columns and needed fields.

3. Construct Query

  • SELECT - Columns and aggregates
  • FROM/JOIN - Connect tables on FK = PK
  • WHERE - Filters before aggregation
  • GROUP BY - All non-aggregate columns
  • ORDER BY - Sort meaningfully
  • LIMIT - Default 5 rows

4. Validate and Execute

Check all JOINs have conditions, GROUP BY is correct, then run query.

Example: Revenue by Country

SELECT
    c.Country,
    ROUND(SUM(i.Total), 2) as TotalRevenue
FROM Invoice i
INNER JOIN Customer c ON i.CustomerId = c.CustomerId
GROUP BY c.Country
ORDER BY TotalRevenue DESC
LIMIT 5;

Error Recovery

If a query fails or returns unexpected results:

  1. Empty results — Verify column names and WHERE conditions against the schema; check for case sensitivity or NULL values
  2. Syntax error — Re-examine JOINs, GROUP BY completeness, and alias references
  3. Timeout — Add stricter WHERE filters or LIMIT to reduce result set, then refine

Quality Guidelines

  • Query only relevant columns (not SELECT *)
  • Always apply LIMIT (5 default)
  • Use table aliases for clarity
  • For complex queries: use write_todos to plan
  • Never use DML statements (INSERT, UPDATE, DELETE, DROP)