expression: let expression.Column take Sel into account wh… (ping…

…cap#12693)

expression/builtin_vectorized_test.go

@@ -764,6 +764,26 @@ func (s *testEvaluatorSuite) TestFloat32ColVec(c *C) {
 		c.Assert(v, Equals, result.GetFloat64(i))
 		i++
 	}
+
+	// set Sel
+	n := chk.NumRows()
+	sel := make([]int, n/2)
+	for i := 0; i < n; i += 2 {
+		sel = append(sel, i)
+	}
+	chk.SetSel(sel)
+	c.Assert(col.VecEvalReal(ctx, chk, result), IsNil)
+	i = 0
+	for row := it.Begin(); row != it.End(); row = it.Next() {
+		v, _, err := col.EvalReal(ctx, row)
+		c.Assert(err, IsNil)
+		c.Assert(v, Equals, result.GetFloat64(i))
+		i++
+	}
+
+	// set an empty Sel
+	sel = sel[:0]
+	c.Assert(col.VecEvalReal(ctx, chk, result), IsNil)
 }
 
 func BenchmarkFloat32ColRow(b *testing.B) {

expression/column.go

@@ -246,6 +246,17 @@ func (col *Column) VecEvalReal(ctx sessionctx.Context, input *chunk.Chunk, resul
 		result.ResizeFloat64(n, false)
 		f32s := src.Float32s()
 		f64s := result.Float64s()
+		sel := input.Sel()
+		if sel != nil {
+			for i, j := range sel {
+				if src.IsNull(j) {
+					result.SetNull(i, true)
+				} else {
+					f64s[i] = float64(f32s[j])
+				}
+			}
+			return nil
+		}
 		for i := range f32s {
 			// TODO(zhangyuanjia): speed up the way to manipulate null-bitmaps.
 			if src.IsNull(i) {