diff --git a/query/execute/table.go b/query/execute/table.go
index 3f77d445f7..4e69b472fd 100644
--- a/query/execute/table.go
+++ b/query/execute/table.go
@@ -179,7 +179,7 @@ func AppendCol(bj, cj int, cr query.ColReader, builder TableBuilder) {
 	}
 }
 
-// AppendMappedRecord appends the record from cr onto builder assuming matching columns.
+// AppendRecord appends the record from cr onto builder assuming matching columns.
 func AppendRecord(i int, cr query.ColReader, builder TableBuilder) {
 	for j, c := range builder.Cols() {
 		switch c.Type {
@@ -223,6 +223,23 @@ func AppendMappedRecord(i int, cr query.ColReader, builder TableBuilder, colMap
 	}
 }
 
+// ColMap writes a mapping of builder index to column reader index into colMap.
+// When colMap does not have enough capacity a new colMap is allocated.
+// The colMap is always returned
+func ColMap(colMap []int, builder TableBuilder, cr query.ColReader) []int {
+	l := len(builder.Cols())
+	if cap(colMap) < l {
+		colMap = make([]int, len(builder.Cols()))
+	} else {
+		colMap = colMap[:l]
+	}
+	cols := cr.Cols()
+	for j, c := range builder.Cols() {
+		colMap[j] = ColIdx(c.Label, cols)
+	}
+	return colMap
+}
+
 // AppendRecordForCols appends the only the columns provided from cr onto builder.
 func AppendRecordForCols(i int, cr query.ColReader, builder TableBuilder, cols []query.ColMeta) {
 	for j, c := range cols {
diff --git a/query/functions/group.go b/query/functions/group.go
index ee61aba5cc..07518745d4 100644
--- a/query/functions/group.go
+++ b/query/functions/group.go
@@ -303,6 +303,7 @@ func (t *groupTransformation) Process(id execute.DatasetID, tbl query.Table) err
 			on[c.Label] = true
 		}
 	}
+	colMap := make([]int, 0, len(tbl.Cols()))
 	return tbl.Do(func(cr query.ColReader) error {
 		l := cr.Len()
 		for i := 0; i < l; i++ {
@@ -311,7 +312,8 @@ func (t *groupTransformation) Process(id execute.DatasetID, tbl query.Table) err
 			if created {
 				execute.AddTableCols(tbl, builder)
 			}
-			execute.AppendRecord(i, cr, builder)
+			colMap = execute.ColMap(colMap, builder, cr)
+			execute.AppendMappedRecord(i, cr, builder, colMap)
 		}
 		return nil
 	})
diff --git a/query/functions/group_test.go b/query/functions/group_test.go
index ed2ab6d42d..6d0418af73 100644
--- a/query/functions/group_test.go
+++ b/query/functions/group_test.go
@@ -206,6 +206,96 @@ func TestGroup_Process(t *testing.T) {
 				},
 			},
 		},
+		{
+			// TODO(nathanielc): When we have support for null, the missing column
+			// needs to be added with null values for any missing values.
+			// Right now the order of input tables determines whether the column is included.
+			name: "fan in missing columns",
+			spec: &functions.GroupProcedureSpec{
+				GroupMode: functions.GroupModeBy,
+				GroupKeys: []string{"t1"},
+			},
+			data: []query.Table{
+				&executetest.Table{
+					KeyCols: []string{"t1", "t2"},
+					ColMeta: []query.ColMeta{
+						{Label: "_time", Type: query.TTime},
+						{Label: "_value", Type: query.TFloat},
+						{Label: "t1", Type: query.TString},
+						{Label: "t2", Type: query.TString},
+					},
+					Data: [][]interface{}{
+						{execute.Time(2), 1.0, "a", "y"},
+					},
+				},
+				&executetest.Table{
+					KeyCols: []string{"t1", "t3", "t2"},
+					ColMeta: []query.ColMeta{
+						{Label: "_time", Type: query.TTime},
+						{Label: "_value", Type: query.TFloat},
+						{Label: "t1", Type: query.TString},
+						{Label: "t3", Type: query.TInt},
+						{Label: "t2", Type: query.TString},
+					},
+					Data: [][]interface{}{
+						{execute.Time(1), 2.0, "a", int64(5), "x"},
+					},
+				},
+				&executetest.Table{
+					KeyCols: []string{"t1", "t2"},
+					ColMeta: []query.ColMeta{
+						{Label: "_time", Type: query.TTime},
+						{Label: "_value", Type: query.TFloat},
+						{Label: "t1", Type: query.TString},
+						{Label: "t2", Type: query.TString},
+					},
+					Data: [][]interface{}{
+						{execute.Time(2), 7.0, "b", "y"},
+					},
+				},
+				&executetest.Table{
+					KeyCols: []string{"t1", "t3", "t2"},
+					ColMeta: []query.ColMeta{
+						{Label: "_time", Type: query.TTime},
+						{Label: "_value", Type: query.TFloat},
+						{Label: "t1", Type: query.TString},
+						{Label: "t3", Type: query.TInt},
+						{Label: "t2", Type: query.TString},
+					},
+					Data: [][]interface{}{
+						{execute.Time(1), 4.0, "b", int64(7), "x"},
+					},
+				},
+			},
+			want: []*executetest.Table{
+				{
+					KeyCols: []string{"t1"},
+					ColMeta: []query.ColMeta{
+						{Label: "_time", Type: query.TTime},
+						{Label: "_value", Type: query.TFloat},
+						{Label: "t1", Type: query.TString},
+						{Label: "t2", Type: query.TString},
+					},
+					Data: [][]interface{}{
+						{execute.Time(2), 1.0, "a", "y"},
+						{execute.Time(1), 2.0, "a", "x"},
+					},
+				},
+				{
+					KeyCols: []string{"t1"},
+					ColMeta: []query.ColMeta{
+						{Label: "_time", Type: query.TTime},
+						{Label: "_value", Type: query.TFloat},
+						{Label: "t1", Type: query.TString},
+						{Label: "t2", Type: query.TString},
+					},
+					Data: [][]interface{}{
+						{execute.Time(2), 7.0, "b", "y"},
+						{execute.Time(1), 4.0, "b", "x"},
+					},
+				},
+			},
+		},
 		{
 			name: "fan out",
 			spec: &functions.GroupProcedureSpec{