proc addIndexString(column: Column; table: Table): string {....raises: [],
    tags: [], forbids: [].}

proc changeColumnString(table: Table; column: Column): seq[string] {.
    ...raises: [DbError, KeyError], tags: [], forbids: [].}

proc changeForeignKey(column: Column; table: Table): string {.
    ...raises: [KeyError], tags: [], forbids: [].}