From 69f274915412d3b24e1d182decb26686a119cdc9 Mon Sep 17 00:00:00 2001
From: Kenan Yao <cauchy1992@gmail.com>
Date: Thu, 28 Feb 2019 13:06:38 +0800
Subject: [PATCH] executor: only show valid columns in `stats_histogram`
 (#9487)

---
 executor/show_stats.go      |  4 ++++
 executor/show_stats_test.go | 15 ++++++++++++++-
 statistics/table.go         |  2 +-
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/executor/show_stats.go b/executor/show_stats.go
index c63286e6a8337..b5410c360fdcd 100644
--- a/executor/show_stats.go
+++ b/executor/show_stats.go
@@ -82,6 +82,10 @@ func (e *ShowExec) appendTableForStatsHistograms(dbName, tblName, partitionName
 		return
 	}
 	for _, col := range statsTbl.Columns {
+		// Pass a nil StatementContext to avoid column stats being marked as needed.
+		if col.IsInvalid(nil, false) {
+			continue
+		}
 		e.histogramToRow(dbName, tblName, partitionName, col.Info.Name.O, 0, col.Histogram, col.AvgColSize(statsTbl.Count))
 	}
 	for _, idx := range statsTbl.Indices {
diff --git a/executor/show_stats_test.go b/executor/show_stats_test.go
index dcb9139073b72..2786ac65498ef 100644
--- a/executor/show_stats_test.go
+++ b/executor/show_stats_test.go
@@ -40,13 +40,26 @@ func (s *testSuite1) TestShowStatsHistograms(c *C) {
 	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t (a int, b int)")
 	tk.MustExec("analyze table t")
-	result := tk.MustQuery("show stats_histograms").Sort()
+	result := tk.MustQuery("show stats_histograms")
+	c.Assert(len(result.Rows()), Equals, 0)
+	tk.MustExec("insert into t values(1,1)")
+	tk.MustExec("analyze table t")
+	result = tk.MustQuery("show stats_histograms").Sort()
 	c.Assert(len(result.Rows()), Equals, 2)
 	c.Assert(result.Rows()[0][3], Equals, "a")
 	c.Assert(result.Rows()[1][3], Equals, "b")
 	result = tk.MustQuery("show stats_histograms where column_name = 'a'")
 	c.Assert(len(result.Rows()), Equals, 1)
 	c.Assert(result.Rows()[0][3], Equals, "a")
+
+	tk.MustExec("drop table t")
+	tk.MustExec("create table t(a int, b int, c int, index idx_b(b), index idx_c_a(c, a))")
+	tk.MustExec("insert into t values(1,null,1),(2,null,2),(3,3,3),(4,null,4),(null,null,null)")
+	res := tk.MustQuery("show stats_histograms where table_name = 't'")
+	c.Assert(len(res.Rows()), Equals, 0)
+	tk.MustExec("analyze table t index idx_b")
+	res = tk.MustQuery("show stats_histograms where table_name = 't' and column_name = 'idx_b'")
+	c.Assert(len(res.Rows()), Equals, 1)
 }
 
 func (s *testSuite1) TestShowStatsBuckets(c *C) {
diff --git a/statistics/table.go b/statistics/table.go
index 7f59926fd1d56..2110a13bdbd06 100644
--- a/statistics/table.go
+++ b/statistics/table.go
@@ -351,7 +351,7 @@ func (c *Column) IsInvalid(sc *stmtctx.StatementContext, collPseudo bool) bool {
 	if collPseudo && c.NotAccurate() {
 		return true
 	}
-	if c.NDV > 0 && c.Len() == 0 {
+	if c.NDV > 0 && c.Len() == 0 && sc != nil {
 		sc.SetHistogramsNotLoad()
 		histogramNeededColumns.insert(tableColumnID{tableID: c.PhysicalID, columnID: c.Info.ID})
 	}