Function CheckModifyTypeCompatible

pkg/types/field_type.go:1473–1530

CheckModifyTypeCompatible checks whether changes column type to another is compatible and can be changed. If types are compatible and can be directly changed, nil err will be returned; otherwise the types are incompatible. There are two cases when types incompatible: 1. returned canReorg == true: ty

(origin *FieldType, to *FieldType)

// 1. returned canReorg == true: types can be changed by reorg
// 2. returned canReorg == false: type change not supported yet
func CheckModifyTypeCompatible(origin *FieldType, to *FieldType) (canReorg bool, err error) {
	// Deal with the same type.
	if origin.GetType() == to.GetType() {
		if origin.GetType() == mysql.TypeEnum || origin.GetType() == mysql.TypeSet {
			typeVar := "set"
			if origin.GetType() == mysql.TypeEnum {
				typeVar = "enum"
			}
			if len(to.GetElems()) < len(origin.GetElems()) {
				msg := fmt.Sprintf("the number of %s column's elements is less than the original: %d", typeVar, len(origin.GetElems()))
				return true, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(msg)
			}
			for index, originElem := range origin.GetElems() {
				toElem := to.GetElems()[index]
				if originElem != toElem {
					msg := fmt.Sprintf("cannot modify %s column value %s to %s", typeVar, originElem, toElem)
					return true, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(msg)
				}
			}
		}

		if origin.GetType() == mysql.TypeNewDecimal {
			// Floating-point and fixed-point types also can be UNSIGNED. As with integer types, this attribute prevents
			// negative values from being stored in the column. Unlike the integer types, the upper range of column values
			// remains the same.
			if to.GetFlen() != origin.GetFlen() || to.GetDecimal() != origin.GetDecimal() || mysql.HasUnsignedFlag(to.GetFlag()) != mysql.HasUnsignedFlag(origin.GetFlag()) {
				msg := fmt.Sprintf("decimal change from decimal(%d, %d) to decimal(%d, %d)", origin.GetFlen(), origin.GetDecimal(), to.GetFlen(), to.GetDecimal())
				return true, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(msg)
			}
		}

		needReorg, reason := needReorgToChange(origin, to)
		if !needReorg {
			return false, nil
		}
		return true, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(reason)
	}

	// Deal with the different type.
	if !checkTypeChangeSupported(origin, to) {
		unsupportedMsg := fmt.Sprintf("change from original type %v to %v is currently unsupported yet", origin.CompactStr(), to.CompactStr())
		return false, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(unsupportedMsg)
	}

	// Check if different type can directly convert and no need to reorg.
	stringToString := IsString(origin.GetType()) && IsString(to.GetType())
	integerToInteger := mysql.IsIntegerType(origin.GetType()) && mysql.IsIntegerType(to.GetType())
	if stringToString || integerToInteger {
		needReorg, reason := needReorgToChange(origin, to)
		if !needReorg {
			return false, nil
		}
		return true, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(reason)
	}

	notCompatibleMsg := fmt.Sprintf("type %v not match origin %v", to.CompactStr(), origin.CompactStr())
	return true, dbterror.ErrUnsupportedModifyColumn.GenWithStackByArgs(notCompatibleMsg)
}