describe_table

Instructions

Retrieves column definitions, primary keys, foreign keys, and indexes.

Args:
    table: Table name, optionally with schema (e.g., 'dbo.Users' or 'Users').
           Defaults to 'dbo' schema if not specified.

Returns:
    Dictionary with:
    - table: Full table name (schema.table)
    - columns: List of column info (name, type, nullable, etc.)
    - primary_key: List of primary key column names
    - foreign_keys: List of foreign key relationships
    - indexes: List of index info

Implementation Reference

• src/mssql_mcp/tools/tables.py:81-216 (handler)

  The core handler function for the 'describe_table' MCP tool. Decorated with @mcp.tool() for automatic registration. Executes SQL queries against MSSQL INFORMATION_SCHEMA and sys tables to retrieve comprehensive table metadata including columns, primary keys, foreign keys, and indexes. Handles parsing of table name, error handling, and formats output as a structured dictionary.

  @mcp.tool()
  def describe_table(table: str) -> dict[str, Any]:
      """Get detailed column information for a table.
  
      Retrieves column definitions, primary keys, foreign keys, and indexes.
  
      Args:
          table: Table name, optionally with schema (e.g., 'dbo.Users' or 'Users').
                 Defaults to 'dbo' schema if not specified.
  
      Returns:
          Dictionary with:
          - table: Full table name (schema.table)
          - columns: List of column info (name, type, nullable, etc.)
          - primary_key: List of primary key column names
          - foreign_keys: List of foreign key relationships
          - indexes: List of index info
      """
      try:
          manager = get_connection_manager()
          schema, table_name = parse_table_name(table)
  
          # Get columns
          columns_query = """
              SELECT
                  COLUMN_NAME as [name],
                  DATA_TYPE as [type],
                  CHARACTER_MAXIMUM_LENGTH as [max_length],
                  NUMERIC_PRECISION as [precision],
                  NUMERIC_SCALE as [scale],
                  IS_NULLABLE as [nullable],
                  COLUMN_DEFAULT as [default_value]
              FROM INFORMATION_SCHEMA.COLUMNS
              WHERE TABLE_SCHEMA = %s AND TABLE_NAME = %s
              ORDER BY ORDINAL_POSITION
          """
          columns_rows = manager.execute_query(columns_query, (schema, table_name))
  
          columns = []
          for row in columns_rows:
              col_info: dict[str, Any] = {
                  "name": row["name"],
                  "type": row["type"],
                  "nullable": row["nullable"] == "YES",
              }
              if row["max_length"]:
                  col_info["max_length"] = row["max_length"]
              if row["precision"]:
                  col_info["precision"] = row["precision"]
              if row["scale"]:
                  col_info["scale"] = row["scale"]
              if row["default_value"]:
                  col_info["default"] = row["default_value"]
              columns.append(col_info)
  
          # Get primary key columns
          pk_query = """
              SELECT c.COLUMN_NAME
              FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc
              JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
                  ON tc.CONSTRAINT_NAME = c.CONSTRAINT_NAME
                  AND tc.TABLE_SCHEMA = c.TABLE_SCHEMA
                  AND tc.TABLE_NAME = c.TABLE_NAME
              WHERE tc.TABLE_SCHEMA = %s
                  AND tc.TABLE_NAME = %s
                  AND tc.CONSTRAINT_TYPE = 'PRIMARY KEY'
              ORDER BY c.ORDINAL_POSITION
          """
          pk_rows = manager.execute_query(pk_query, (schema, table_name))
          primary_key = [row["COLUMN_NAME"] for row in pk_rows]
  
          # Get foreign keys
          fk_query = """
              SELECT
                  fk.name as constraint_name,
                  COL_NAME(fkc.parent_object_id, fkc.parent_column_id) as [column],
                  OBJECT_SCHEMA_NAME(fkc.referenced_object_id) as ref_schema,
                  OBJECT_NAME(fkc.referenced_object_id) as ref_table,
                  COL_NAME(fkc.referenced_object_id, fkc.referenced_column_id) as ref_column
              FROM sys.foreign_keys fk
              JOIN sys.foreign_key_columns fkc ON fk.object_id = fkc.constraint_object_id
              WHERE fk.parent_object_id = OBJECT_ID(%s)
              ORDER BY fk.name, fkc.constraint_column_id
          """
          fk_rows = manager.execute_query(fk_query, (f"{schema}.{table_name}",))
  
          foreign_keys = [
              {
                  "constraint": row["constraint_name"],
                  "column": row["column"],
                  "references_table": f"{row['ref_schema']}.{row['ref_table']}",
                  "references_column": row["ref_column"],
              }
              for row in fk_rows
          ]
  
          # Get indexes
          idx_query = """
              SELECT
                  i.name as index_name,
                  i.type_desc as [type],
                  i.is_unique,
                  i.is_primary_key,
                  STRING_AGG(c.name, ', ') WITHIN GROUP (ORDER BY ic.key_ordinal) as [columns]
              FROM sys.indexes i
              JOIN sys.index_columns ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id
              JOIN sys.columns c ON ic.object_id = c.object_id AND ic.column_id = c.column_id
              WHERE i.object_id = OBJECT_ID(%s)
                  AND i.name IS NOT NULL
              GROUP BY i.name, i.type_desc, i.is_unique, i.is_primary_key
              ORDER BY i.name
          """
          idx_rows = manager.execute_query(idx_query, (f"{schema}.{table_name}",))
  
          indexes = [
              {
                  "name": row["index_name"],
                  "type": row["type"],
                  "is_unique": bool(row["is_unique"]),
                  "is_primary_key": bool(row["is_primary_key"]),
                  "columns": row["columns"],
              }
              for row in idx_rows
          ]
  
          return {
              "table": f"{schema}.{table_name}",
              "columns": columns,
              "primary_key": primary_key,
              "foreign_keys": foreign_keys,
              "indexes": indexes,
          }
  
      except Exception as e:
          logger.error(f"Error describing table {table}: {e}")
          return {"error": str(e)}