func executeLine(tx *sql.Tx, txnLine string) error {
    if tidb.IsQuery(txnLine) {
        rows, err := tx.Query(txnLine)
        if err != nil {
            return errors.Trace(err)
        }
        defer rows.Close()
        cols, err := rows.Columns()
        if err != nil {
            return errors.Trace(err)
        }

        values := make([][]byte, len(cols))
        scanArgs := make([]interface{}, len(values))
        for i := range values {
            scanArgs[i] = &values[i]
        }

        var datas [][]string
        for rows.Next() {
            err := rows.Scan(scanArgs...)
            if err != nil {
                return errors.Trace(err)
            }

            data := make([]string, len(cols))
            for i, value := range values {
                if value == nil {
                    data[i] = "NULL"
                } else {
                    data[i] = string(value)
                }
            }

            datas = append(datas, data)
        }

        // For `cols` and `datas[i]` always has the same length,
        // no need to check return validity.
        result, _ := printer.GetPrintResult(cols, datas)
        fmt.Printf("%s", result)

        if err := rows.Err(); err != nil {
            return errors.Trace(err)
        }
    } else {
        // TODO: rows affected and last insert id
        _, err := tx.Exec(txnLine)
        if err != nil {
            return errors.Trace(err)
        }
    }
    return nil
}