stats: fix panic caused by empty histogram (#7912) (#7928)

pingcap · Oct 17, 2018 · c91290f · c91290f
1 parent 62a6be9
commit c91290f
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Showing 2 changed files with 14 additions and 2 deletions.
diff --git a/statistics/histogram.go b/statistics/histogram.go
@@ -679,7 +679,7 @@ func (hg *Histogram) AvgCountPerValue(totalCount int64) float64 {
 }
 
 func (hg *Histogram) outOfRange(val types.Datum) bool {
-	if hg.Bounds == nil {
+	if hg.Len() == 0 {
 		return true
 	}
 	return chunk.Compare(hg.Bounds.GetRow(0), 0, &val) > 0 ||
@@ -858,7 +858,7 @@ func (idx *Index) getRowCount(sc *stmtctx.StatementContext, indexRanges []*range
 }
 
 func (idx *Index) outOfRange(val types.Datum) bool {
-	if idx.Bounds == nil {
+	if idx.Histogram.Len() == 0 {
 		return true
 	}
 	withInLowBoundOrPrefixMatch := chunk.Compare(idx.Bounds.GetRow(0), 0, &val) <= 0 ||

diff --git a/statistics/selectivity_test.go b/statistics/selectivity_test.go
@@ -292,6 +292,18 @@ func (s *testSelectivitySuite) TestEstimationForUnknownValues(c *C) {
 	count, err = statsTbl.GetRowCountByIndexRanges(sc, idxID, getRange(9, 30))
 	c.Assert(err, IsNil)
 	c.Assert(count, Equals, 2.2)
+
+	testKit.MustExec("truncate table t")
+	testKit.MustExec("insert into t values (null, null)")
+	testKit.MustExec("analyze table t")
+	table, err = s.dom.InfoSchema().TableByName(model.NewCIStr("test"), model.NewCIStr("t"))
+	c.Assert(err, IsNil)
+	statsTbl = h.GetTableStats(table.Meta())
+
+	colID = table.Meta().Columns[0].ID
+	count, err = statsTbl.GetRowCountByColumnRanges(sc, colID, getRange(1, 30))
+	c.Assert(err, IsNil)
+	c.Assert(count, Equals, 0.0)
 }
 
 func BenchmarkSelectivity(b *testing.B) {