expression: return null for empty time format (#67538)

close #59445

Author: hawkingrei

pkg/expression/builtin_time.go

@@ -6477,6 +6477,9 @@ func (b *builtinTimeFormatSig) evalString(ctx EvalContext, row chunk.Row) (strin
 	if err != nil || isNull {
 		return "", isNull, err
 	}
+	if len(formatMask) == 0 {
+		return "", true, nil
+	}
 	res, err := b.formatTime(dur, formatMask)
 	return res, isNull, err
 }

pkg/expression/builtin_time_test.go

@@ -3069,6 +3069,14 @@ func TestTimeFormat(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, true, v.IsNull())
 
+	// issue:59445
+	args = []types.Datum{types.NewStringDatum("12:34:56"), types.NewStringDatum("")}
+	f, err = fc.getFunction(ctx, datumsToConstants(args))
+	require.NoError(t, err)
+	v, err = evalBuiltinFunc(f, ctx, chunk.Row{})
+	require.NoError(t, err)
+	require.True(t, v.IsNull())
+
 	tblDate := []struct {
 		Input  []string
 		Expect any

pkg/expression/builtin_time_vec.go

@@ -374,6 +374,10 @@ func (b *builtinTimeFormatSig) vecEvalString(ctx EvalContext, input *chunk.Chunk
 			result.AppendNull()
 			continue
 		}
+		if len(buf1.GetString(i)) == 0 {
+			result.AppendNull()
+			continue
+		}
 		res, err := b.formatTime(buf.GetDuration(i, 0), buf1.GetString(i))
 		if err != nil {
 			return err

pkg/expression/builtin_time_vec_test.go

@@ -18,6 +18,7 @@ import (
 	"math"
 	"math/rand"
 	"testing"
+	"time"
 
 	"github.com/pingcap/tidb/pkg/parser/ast"
 	"github.com/pingcap/tidb/pkg/parser/mysql"
@@ -569,6 +570,33 @@ func TestVectorizedBuiltinTimeFunc(t *testing.T) {
 	testVectorizedBuiltinFunc(t, vecBuiltinTimeCases)
 }
 
+func TestVectorizedTimeFormatEmptyFormatReturnsNull(t *testing.T) {
+	ctx := createContext(t)
+
+	durationType := types.NewFieldType(mysql.TypeDuration)
+	durationType.SetDecimal(types.DefaultFsp)
+	formatType := types.NewFieldType(mysql.TypeString)
+
+	col0 := &Column{RetType: durationType, Index: 0}
+	col1 := &Column{RetType: formatType, Index: 1}
+	f, err := funcs[ast.TimeFormat].getFunction(ctx, []Expression{col0, col1})
+	require.NoError(t, err)
+	require.True(t, f.vectorized() && f.isChildrenVectorized())
+
+	input := chunk.NewChunkWithCapacity([]*types.FieldType{durationType, formatType}, 2)
+	input.AppendDuration(0, types.Duration{Duration: 12*time.Hour + 34*time.Minute + 56*time.Second, Fsp: types.DefaultFsp})
+	input.AppendString(1, "")
+	input.AppendDuration(0, types.Duration{Duration: time.Hour + 2*time.Minute + 3*time.Second, Fsp: types.DefaultFsp})
+	input.AppendString(1, "%H:%i:%s")
+
+	result := chunk.NewColumn(formatType, 2)
+	require.NoError(t, vecEvalType(ctx, f, types.ETString, input, result))
+	require.Equal(t, 2, result.Rows())
+	require.True(t, result.IsNull(0))
+	require.False(t, result.IsNull(1))
+	require.Equal(t, "01:02:03", result.GetString(1))
+}
+
 func BenchmarkVectorizedBuiltinTimeEvalOneVec(b *testing.B) {
 	benchmarkVectorizedEvalOneVec(b, vecBuiltinTimeCases)
 }