code: func IntergerSignedLowerBound(intType byte) int64 {
  	switch intType {
  	case mysql.TypeTiny:
  		return math.MinInt8
  	case mysql.TypeShort:
  		return math.MinInt16
  	case mysql.TypeInt24:
  		return mysql.MinInt24
  	case mysql.TypeLong:
  		return math.MinInt32
  	case mysql.TypeLonglong:
  		return math.MinInt64
  	default:
  		panic("Input byte is not a mysql type")
  	}
  }
docs: // IntergerSignedLowerBound indicates the min int64 values of different mysql types.