func compareFloatString(a float64, s string) (int, error) {
// MySQL will convert string to a float point value
// MySQL use a very loose conversation, e.g, 123.abc -> 123
// we should do a trade off whether supporting this feature or using a strict mode
// now we use a strict mode
b, err := types.StrToFloat(s)
if err != nil {
return 0, err
}
return types.CompareFloat64(a, b), nil
}
// See https://dev.mysql.com/doc/refman/5.7/en/type-conversion.html
func evalCompare(a interface{}, b interface{}) (int, error) {
// TODO: support compare time type with other types
switch x := a.(type) {
case float64:
switch y := b.(type) {
case float64:
return types.CompareFloat64(x, y), nil
case string:
return compareFloatString(x, y)
}
case int64:
switch y := b.(type) {
case int64:
return types.CompareInt64(x, y), nil
case uint64:
return types.CompareInteger(x, y), nil
case string:
return compareFloatString(float64(x), y)
}
case uint64:
switch y := b.(type) {
case uint64:
return types.CompareUint64(x, y), nil
case int64:
return -types.CompareInteger(y, x), nil
case string:
return compareFloatString(float64(x), y)
}
case mysql.Decimal:
switch y := b.(type) {
case mysql.Decimal:
return x.Cmp(y), nil
case string:
f, err := mysql.ConvertToDecimal(y)
if err != nil {
return 0, err
}
return x.Cmp(f), nil
}
case string:
switch y := b.(type) {
case string:
return types.CompareString(x, y), nil
case int64:
return compareStringFloat(x, float64(y))
case uint64:
return compareStringFloat(x, float64(y))
case float64:
return compareStringFloat(x, y)
case mysql.Decimal:
f, err := mysql.ConvertToDecimal(x)
if err != nil {
return 0, err
}
return f.Cmp(y), nil
case mysql.Time:
n, err := y.CompareString(x)
return -n, err
case mysql.Duration:
n, err := y.CompareString(x)
return -n, err
}
case mysql.Time:
switch y := b.(type) {
case mysql.Time:
return x.Compare(y), nil
case string:
return x.CompareString(y)
}
case mysql.Duration:
switch y := b.(type) {
case mysql.Duration:
return x.Compare(y), nil
case string:
return x.CompareString(y)
}
}
return 0, errors.Errorf("invalid compare type %T cmp %T", a, b)
}