explicitly cast to max precision for comparisons

Author: angelamayxie

sql/expression/comparison.go

@@ -222,11 +222,7 @@ func (c *comparison) castLeftAndRight(ctx *sql.Context, left, right interface{})
 	}
 
 	if types.IsTime(leftType) || types.IsTime(rightType) {
-		l, _, err := types.DatetimeMaxPrecision.Convert(ctx, left)
-		if err != nil {
-			return nil, nil, nil, err
-		}
-		r, _, err := types.DatetimeMaxPrecision.Convert(ctx, right)
+		l, r, err := convertLeftAndRight(ctx, left, right, ConvertToDatetime)
 		if err != nil {
 			return nil, nil, nil, err
 		}
@@ -305,13 +301,16 @@ func (c *comparison) castLeftAndRight(ctx *sql.Context, left, right interface{})
 }
 
 func convertLeftAndRight(ctx *sql.Context, left, right interface{}, convertTo string) (interface{}, interface{}, error) {
-	// TODO: typeLength and typeScale should be the actual length and scale of the type to be converted
-	l, err := convertValue(ctx, left, convertTo, nil, 0, 0)
+	typeLength := 0
+	if convertTo == ConvertToDatetime {
+		typeLength = types.MaxDatetimePrecision
+	}
+	l, err := convertValue(ctx, left, convertTo, nil, typeLength, 0)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	r, err := convertValue(ctx, right, convertTo, nil, 0, 0)
+	r, err := convertValue(ctx, right, convertTo, nil, typeLength, 0)
 	if err != nil {
 		return nil, nil, err
 	}

sql/types/datetime.go

@@ -36,6 +36,8 @@ const ZeroTimestampDatetimeStr = "0000-00-00 00:00:00"
 
 const MinDatetimeStringLength = 8 // length of "2000-1-1"
 
+const MaxDatetimePrecision = 6
+
 var (
 	// ErrConvertingToTime is thrown when a value cannot be converted to a Time
 	ErrConvertingToTime = errors.NewKind("Incorrect datetime value: '%v'")
@@ -105,13 +107,13 @@ var (
 	// DatetimeDefaultPrecision is a date and a time without a specified precision
 	DatetimeDefaultPrecision = MustCreateDatetimeType(sqltypes.Datetime, 0)
 	// DatetimeMaxPrecision is a date and a time with maximum precision
-	DatetimeMaxPrecision = MustCreateDatetimeType(sqltypes.Datetime, 6)
+	DatetimeMaxPrecision = MustCreateDatetimeType(sqltypes.Datetime, MaxDatetimePrecision)
 	// Timestamp is a UNIX timestamp with default precision (no fractional seconds).
 	Timestamp = MustCreateDatetimeType(sqltypes.Timestamp, 0)
 	// TimestampMaxPrecision is a UNIX timestamp with maximum precision
-	TimestampMaxPrecision = MustCreateDatetimeType(sqltypes.Timestamp, 6)
+	TimestampMaxPrecision = MustCreateDatetimeType(sqltypes.Timestamp, MaxDatetimePrecision)
 	// DatetimeMaxRange is a date and a time with maximum precision and maximum range.
-	DatetimeMaxRange = MustCreateDatetimeType(sqltypes.Datetime, 6)
+	DatetimeMaxRange = MustCreateDatetimeType(sqltypes.Datetime, MaxDatetimePrecision)
 
 	datetimeValueType = reflect.TypeOf(time.Time{})
 )
@@ -128,7 +130,7 @@ var _ sql.CollationCoercible = datetimeType{}
 func CreateDatetimeType(baseType query.Type, precision int) (sql.DatetimeType, error) {
 	switch baseType {
 	case sqltypes.Date, sqltypes.Datetime, sqltypes.Timestamp:
-		if precision < 0 || precision > 6 {
+		if precision < 0 || precision > MaxDatetimePrecision {
 			return nil, fmt.Errorf("precision must be between 0 and 6, got %d", precision)
 		}
 		return datetimeType{
@@ -221,7 +223,7 @@ func ConvertToTime(ctx context.Context, v interface{}, t datetimeType) (time.Tim
 	}
 
 	// Round the date to the precision of this type
-	if t.precision < 6 {
+	if t.precision < MaxDatetimePrecision {
 		truncationDuration := time.Second / time.Duration(precisionConversion[t.precision])
 		res = res.Round(truncationDuration)
 	} else {