expression: let first_row get the first value no matter if it's null (p…

…ingcap#2057)

ast/functions.go

@@ -531,4 +531,5 @@ type AggEvaluateContext struct {
 	Count           int64
 	Value           types.Datum
 	Buffer          *bytes.Buffer // Buffer is used for group_concat.
+	GotFirstRow     bool          // It will check if the agg has met the first row key.
 }

executor/aggregate_test.go

@@ -78,6 +78,8 @@ func (s *testSuite) TestAggregation(c *C) {
 	result.Check(testkit.Rows("3", "2", "2"))
 	result = tk.MustQuery("select count(*) from t having 1 = 0")
 	result.Check(testkit.Rows())
+	result = tk.MustQuery("select c,d from t group by d")
+	result.Check(testkit.Rows("<nil> 1", "1 2", "1 3"))
 	result = tk.MustQuery("select - c, c as d from t group by c having null not between c and avg(distinct d) - d")
 	result.Check(testkit.Rows())
 	result = tk.MustQuery("select - c as c from t group by c having t.c > 5")
@@ -90,7 +92,7 @@ func (s *testSuite) TestAggregation(c *C) {
 	result = tk.MustQuery("select c as a from t group by d having a < 0")
 	result.Check(testkit.Rows())
 	result = tk.MustQuery("select c as a from t group by d having sum(a) = 2")
-	result.Check(testkit.Rows("1"))
+	result.Check(testkit.Rows("<nil>"))
 	result = tk.MustQuery("select count(distinct c) from t group by d")
 	result.Check(testkit.Rows("1", "2", "2"))
 	result = tk.MustQuery("select sum(c) from t group by d")
@@ -152,7 +154,7 @@ func (s *testSuite) TestAggregation(c *C) {
 	result = tk.MustQuery("select count(*) from t a join t b where a.c < 0")
 	result.Check(testkit.Rows("0"))
 	result = tk.MustQuery("select sum(b.c), count(b.d), a.c from t a left join t b on a.c = b.d group by b.d order by b.d")
-	result.Check(testkit.Rows("<nil> 0 4", "8 12 1", "5 2 3"))
+	result.Check(testkit.Rows("<nil> 0 <nil>", "8 12 1", "5 2 3"))
 	// This two cases prove that having always resolve name from field list firstly.
 	result = tk.MustQuery("select 1-d as d from t having d < 0 order by d desc")
 	result.Check(testkit.Rows("-1", "-1", "-2", "-2"))

expression/aggregation.go

@@ -828,7 +828,7 @@ func (ff *firstRowFunction) GetType() *types.FieldType {
 // Update implements AggregationFunction interface.
 func (ff *firstRowFunction) Update(row []types.Datum, groupKey []byte, ectx context.Context) error {
 	ctx := ff.getContext(groupKey)
-	if !ctx.Value.IsNull() {
+	if ctx.GotFirstRow {
 		return nil
 	}
 	if len(ff.Args) != 1 {
@@ -839,13 +839,14 @@ func (ff *firstRowFunction) Update(row []types.Datum, groupKey []byte, ectx cont
 		return errors.Trace(err)
 	}
 	ctx.Value = value
+	ctx.GotFirstRow = true
 	return nil
 }
 
 // StreamUpdate implements AggregationFunction interface.
 func (ff *firstRowFunction) StreamUpdate(row []types.Datum, ectx context.Context) error {
 	ctx := ff.getStreamedContext()
-	if !ctx.Value.IsNull() {
+	if ctx.GotFirstRow {
 		return nil
 	}
 	if len(ff.Args) != 1 {
@@ -856,6 +857,7 @@ func (ff *firstRowFunction) StreamUpdate(row []types.Datum, ectx context.Context
 		return errors.Trace(err)
 	}
 	ctx.Value = value
+	ctx.GotFirstRow = true
 	return nil
 }
 

store/localstore/local_aggregate.go

@@ -82,10 +82,12 @@ func (rs *localRegion) aggregate(ctx *selectContext, h int64, row map[int64][]by
 type aggItem struct {
 	// Number of rows, this could be used in cout/avg
 	count uint64
-	// This could be used to store sum/max/min
+	// This could be used to store sum/max/min/first
 	value types.Datum
 	// TODO: support group_concat
 	buffer *bytes.Buffer // Buffer is used for group_concat.
+	// It will check if the agg has met the first row key.
+	gotFirstRow bool
 }
 
 // This is similar to ast.AggregateFuncExpr but use tipb.Expr.
@@ -200,13 +202,14 @@ func (n *aggregateFuncExpr) updateCount(ctx *selectContext, args []types.Datum)
 
 func (n *aggregateFuncExpr) updateFirst(ctx *selectContext, args []types.Datum) error {
 	aggItem := n.getAggItem()
-	if !aggItem.value.IsNull() {
+	if aggItem.gotFirstRow {
 		return nil
 	}
 	if len(args) != 1 {
 		return errors.New("Wrong number of args for AggFuncFirstRow")
 	}
 	aggItem.value = args[0]
+	aggItem.gotFirstRow = true
 	return nil
 }
 

store/tikv/mock-tikv/aggregate.go

@@ -86,6 +86,8 @@ type aggItem struct {
 	value types.Datum
 	// TODO: support group_concat
 	buffer *bytes.Buffer // Buffer is used for group_concat.
+	// It will check if the agg has met the first row key.
+	gotFirstRow bool
 }
 
 // This is similar to ast.AggregateFuncExpr but use tipb.Expr.
@@ -200,13 +202,14 @@ func (n *aggregateFuncExpr) updateCount(ctx *selectContext, args []types.Datum)
 
 func (n *aggregateFuncExpr) updateFirst(ctx *selectContext, args []types.Datum) error {
 	aggItem := n.getAggItem()
-	if !aggItem.value.IsNull() {
+	if aggItem.gotFirstRow {
 		return nil
 	}
 	if len(args) != 1 {
 		return errors.New("Wrong number of args for AggFuncFirstRow")
 	}
 	aggItem.value = args[0]
+	aggItem.gotFirstRow = true
 	return nil
 }