executor: only show valid columns in stats_histogram (#9487) (#9503)

Author: eurekaka

executor/show_stats.go

@@ -54,6 +54,10 @@ func (e *ShowExec) fetchShowStatsHistogram() error {
 			statsTbl := h.GetTableStats(tbl)
 			if !statsTbl.Pseudo {
 				for _, col := range statsTbl.Columns {
+					// Pass a nil StatementContext to avoid column stats being marked as needed.
+					if statsTbl.ColumnIsInvalid(nil, col.ID) {
+						continue
+					}
 					e.histogramToRow(db.Name.O, tbl.Name.O, col.Info.Name.O, 0, col.Histogram, col.AvgColSize(statsTbl.Count))
 				}
 				for _, idx := range statsTbl.Indices {

executor/show_stats_test.go

@@ -41,13 +41,26 @@ func (s *testSuite) 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][2], Equals, "a")
 	c.Assert(result.Rows()[1][2], Equals, "b")
 	result = tk.MustQuery("show stats_histograms where column_name = 'a'")
 	c.Assert(len(result.Rows()), Equals, 1)
 	c.Assert(result.Rows()[0][2], 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 *testSuite) TestShowStatsBuckets(c *C) {

statistics/table.go

@@ -267,7 +267,7 @@ func (t *Table) ColumnIsInvalid(sc *stmtctx.StatementContext, colID int64) bool
 		return true
 	}
 	col, ok := t.Columns[colID]
-	if ok && col.NDV > 0 && col.Len() == 0 {
+	if ok && col.NDV > 0 && col.Len() == 0 && sc != nil {
 		sc.SetHistogramsNotLoad()
 		histogramNeededColumns.insert(tableColumnID{tableID: t.TableID, columnID: colID})
 	}