From 0fefa18f3017e60c724957f57776541979e113d8 Mon Sep 17 00:00:00 2001
From: Haibin Xie <lambdax.tyler@gmail.com>
Date: Mon, 26 Nov 2018 21:08:02 +0800
Subject: [PATCH] stats: fix panic when dumping stats (#8448)

---
 statistics/dump_test.go | 18 ++++++++++++++++++
 statistics/histogram.go |  4 ++--
 statistics/table.go     |  9 +--------
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/statistics/dump_test.go b/statistics/dump_test.go
index c3824d38b88f3..5283855dc0a8d 100644
--- a/statistics/dump_test.go
+++ b/statistics/dump_test.go
@@ -121,3 +121,21 @@ PARTITION BY RANGE ( a ) (
 		assertTableEqual(c, originTables[i], t)
 	}
 }
+
+func (s *testDumpStatsSuite) TestDumpAlteredTable(c *C) {
+	defer cleanEnv(c, s.store, s.do)
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	h := s.do.StatsHandle()
+	oriLease := h.Lease
+	h.Lease = 1
+	defer func() { h.Lease = oriLease }()
+	tk.MustExec("create table t(a int, b int)")
+	tk.MustExec("analyze table t")
+	tk.MustExec("alter table t drop column a")
+	table, err := s.do.InfoSchema().TableByName(model.NewCIStr("test"), model.NewCIStr("t"))
+	c.Assert(err, IsNil)
+	_, err = h.DumpStatsToJSON("test", table.Meta())
+	c.Assert(err, IsNil)
+}
diff --git a/statistics/histogram.go b/statistics/histogram.go
index 54ddbf0a1c97b..67ef41640031d 100644
--- a/statistics/histogram.go
+++ b/statistics/histogram.go
@@ -411,7 +411,7 @@ func (hg *Histogram) greaterAndEqRowCount(value types.Datum) float64 {
 // lessRowCount estimates the row count where the column less than value.
 func (hg *Histogram) lessRowCountWithBktIdx(value types.Datum) (float64, int) {
 	// all the values is null
-	if hg.Bounds == nil {
+	if hg.Bounds.NumRows() == 0 {
 		return 0, 0
 	}
 	index, match := hg.Bounds.LowerBound(0, &value)
@@ -735,7 +735,7 @@ func (c *Column) equalRowCount(sc *stmtctx.StatementContext, val types.Datum, mo
 		return float64(c.NullCount), nil
 	}
 	// all the values is null
-	if c.Histogram.Bounds == nil {
+	if c.Histogram.Bounds.NumRows() == 0 {
 		return 0.0, nil
 	}
 	if c.NDV > 0 && c.outOfRange(val) {
diff --git a/statistics/table.go b/statistics/table.go
index 078b4b9dbd5e3..4d65063143ddc 100644
--- a/statistics/table.go
+++ b/statistics/table.go
@@ -177,14 +177,7 @@ func (h *Handle) columnStatsFromStorage(row chunk.Row, table *Table, tableInfo *
 				return errors.Trace(err)
 			}
 			col = &Column{
-				Histogram: Histogram{
-					ID:                histID,
-					NDV:               distinct,
-					NullCount:         nullCount,
-					tp:                &colInfo.FieldType,
-					LastUpdateVersion: histVer,
-					TotColSize:        totColSize,
-				},
+				Histogram: *NewHistogram(histID, distinct, nullCount, histVer, &colInfo.FieldType, 0, totColSize),
 				Info:      colInfo,
 				Count:     count + nullCount,
 				ErrorRate: errorRate,