evalengine: Fix the min / max calculation for decimals (vitessio#14614)

Signed-off-by: Dirkjan Bussink <[email protected]>

Author: dbussink

go/vt/vtgate/evalengine/api_aggregation.go

@@ -389,6 +389,7 @@ func (s *aggregationDecimal) Min(value sqltypes.Value) error {
 	}
 	if !s.dec.IsInitialized() || dec.Cmp(s.dec) < 0 {
 		s.dec = dec
+		s.prec = -dec.Exponent()
 	}
 	return nil
 }
@@ -403,6 +404,7 @@ func (s *aggregationDecimal) Max(value sqltypes.Value) error {
 	}
 	if !s.dec.IsInitialized() || dec.Cmp(s.dec) > 0 {
 		s.dec = dec
+		s.prec = -dec.Exponent()
 	}
 	return nil
 }

go/vt/vtgate/evalengine/api_aggregation_test.go

@@ -72,6 +72,12 @@ func TestMinMax(t *testing.T) {
 			min:    sqltypes.NewVarBinary("a"),
 			max:    sqltypes.NewVarBinary("b"),
 		},
+		{
+			type_:  sqltypes.Decimal,
+			values: []sqltypes.Value{sqltypes.NewDecimal("1.001"), sqltypes.NewDecimal("2.1")},
+			min:    sqltypes.NewDecimal("1.001"),
+			max:    sqltypes.NewDecimal("2.1"),
+		},
 		{
 			// accent insensitive
 			type_: sqltypes.VarChar,