execute_query

Instructions

Implementation Reference

• src/index.ts:196-222 (handler)

  The main tool handler case for 'execute_query' that extracts arguments (query, database), validates the query is read-only, executes it via the helper, and returns results.

  case "execute_query": {
    console.error('[Tool] Executing execute_query');
    
    const query = request.params.arguments?.query as string;
    const database = request.params.arguments?.database as string | undefined;
    
    if (!query) {
      throw new McpError(ErrorCode.InvalidParams, "Query is required");
    }
    
    // Validate that the query is read-only
    validateQuery(query);
    
    const { rows } = await executeQuery(
      pool,
      query,
      [],
      database
    );
    
    return {
      content: [{
        type: "text",
        text: JSON.stringify(rows, null, 2)
      }]
    };
  }

• src/connection.ts:63-109 (helper)

  The core database query execution function that acquires a connection from the pool, switches database if specified, executes the SQL with a timeout, applies a row limit, and releases the connection.

  export async function executeQuery(
    pool: mysql.Pool,
    sql: string,
    params: any[] = [],
    database?: string
  ): Promise<{ rows: any; fields: mysql.FieldPacket[] }> {
    console.error(`[Query] Executing: ${sql}`);
    
    let connection: mysql.PoolConnection | null = null;
    
    try {
      // Get connection from pool
      connection = await pool.getConnection();
      
      // Use specific database if provided
      if (database) {
        console.error(`[Query] Using database: ${database}`);
        await connection.query(`USE \`${database}\``);
      }
      
      // Execute query with timeout
      const [rows, fields] = await Promise.race([
        connection.query(sql, params),
        new Promise<never>((_, reject) => {
          setTimeout(() => reject(new Error('Query timeout')), DEFAULT_TIMEOUT);
        }),
      ]);
      
      // Apply row limit if result is an array
      const limitedRows = Array.isArray(rows) && rows.length > DEFAULT_ROW_LIMIT
        ? rows.slice(0, DEFAULT_ROW_LIMIT)
        : rows;
      
      // Log result summary
      console.error(`[Query] Success: ${Array.isArray(rows) ? rows.length : 1} rows returned`);
      
      return { rows: limitedRows, fields };
    } catch (error) {
      console.error('[Error] Query execution failed:', error);
      throw error;
    } finally {
      // Release connection back to pool
      if (connection) {
        connection.release();
      }
    }
  }

• src/index.ts:107-124 (registration)

  Tool registration for 'execute_query' within the ListToolsRequestSchema handler, defining name, description, and input schema (query required, database optional).

  {
    name: "execute_query",
    description: "Execute a read-only SQL query",
    inputSchema: {
      type: "object",
      properties: {
        query: {
          type: "string",
          description: "SQL query (only SELECT, SHOW, DESCRIBE, and EXPLAIN statements are allowed)"
        },
        database: {
          type: "string",
          description: "Database name (optional, uses default if not specified)"
        }
      },
      required: ["query"]
    }
  }

• src/validators.ts:79-92 (helper)

  Validation helper that ensures queries are read-only (SELECT, SHOW, DESCRIBE, EXPLAIN only) and rejects write operations. Called by the execute_query handler.

  export function validateQuery(query: string): void {
    console.error('[Validator] Validating query:', query);
    
    if (!query || typeof query !== 'string') {
      throw new Error('Query must be a non-empty string');
    }
    
    if (!isReadOnlyQuery(query)) {
      console.error('[Validator] Query rejected: not read-only');
      throw new Error('Only read-only queries are allowed (SELECT, SHOW, DESCRIBE, EXPLAIN)');
    }
    
    console.error('[Validator] Query validated as read-only');
  }