MCP SQL Server

Instructions

Implementation Reference

• index.js:451-513 (handler)

  The main handler function that implements the logic for the 'describe_table' tool. It queries the database information schema for PostgreSQL or uses DESCRIBE for MySQL to retrieve column information for the specified table.

  async describeTable(tableName) {
    if (!this.currentConfig) {
      throw new Error('Not connected to any database. Call connect_database first.');
    }
  
    if (this.currentConfig.type === 'postgresql') {
      if (!this.postgresPool) {
        throw new Error('PostgreSQL connection not initialized');
      }
  
      const query = `
        SELECT 
          column_name,
          data_type,
          is_nullable,
          column_default
        FROM information_schema.columns
        WHERE table_schema = 'public' AND table_name = $1
        ORDER BY ordinal_position;
      `;
      const result = await this.postgresPool.query(query, [tableName]);
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(
              {
                table: tableName,
                columns: result.rows,
              },
              null,
              2
            ),
          },
        ],
      };
    } else if (this.currentConfig.type === 'mysql') {
      if (!this.mysqlConnection) {
        throw new Error('MySQL connection not initialized');
      }
  
      const [rows] = await this.mysqlConnection.query(
        `DESCRIBE ${tableName}`
      );
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(
              {
                table: tableName,
                columns: rows,
              },
              null,
              2
            ),
          },
        ],
      };
    } else {
      throw new Error(`Unsupported database type: ${this.currentConfig.type}`);
    }
  }

• index.js:186-195 (schema)

  The input schema definition for the 'describe_table' tool, specifying that it requires a 'tableName' string parameter.

  inputSchema: {
    type: 'object',
    properties: {
      tableName: {
        type: 'string',
        description: 'Name of the table to describe',
      },
    },
    required: ['tableName'],
  },

• index.js:183-196 (registration)

  The registration of the 'describe_table' tool in the ListTools response, including name, description, and input schema.

  {
    name: 'describe_table',
    description: 'Get schema information for a specific table',
    inputSchema: {
      type: 'object',
      properties: {
        tableName: {
          type: 'string',
          description: 'Name of the table to describe',
        },
      },
      required: ['tableName'],
    },
  },

• index.js:222-223 (handler)

  The dispatch case in the CallToolRequestSchema handler that invokes the describeTable method for the 'describe_table' tool.

  case 'describe_table':
    return await this.describeTable(args.tableName);