diff --git a/executor/analyze.go b/executor/analyze.go
index 4eb25ba9c7526..7a2b61b2b4bfe 100755
--- a/executor/analyze.go
+++ b/executor/analyze.go
@@ -841,7 +841,7 @@ func (e *AnalyzeFastExec) updateCollectorSamples(sValue []byte, sKey kv.Key, sam
 	for j, idxInfo := range e.idxsInfo {
 		idxVals := make([]types.Datum, 0, len(idxInfo.Columns))
 		for _, idxCol := range idxInfo.Columns {
-			for _, colInfo := range e.colsInfo {
+			for _, colInfo := range e.tblInfo.Columns {
 				if colInfo.Name == idxCol.Name {
 					v, err := e.getValueByInfo(colInfo, values)
 					if err != nil {
diff --git a/executor/analyze_test.go b/executor/analyze_test.go
index b83c677237a91..3ad82874945fa 100644
--- a/executor/analyze_test.go
+++ b/executor/analyze_test.go
@@ -298,6 +298,27 @@ func (s *testSuite1) TestFastAnalyze(c *C) {
 		"test t2  a 0 1 2 1 18446744073709551615 18446744073709551615"))
 }
 
+func (s *testSuite1) TestIssue15751(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t0")
+	tk.MustExec("CREATE TABLE t0(c0 INT, c1 INT, PRIMARY KEY(c0, c1))")
+	tk.MustExec("INSERT INTO t0 VALUES (0, 0)")
+	tk.MustExec("set @@tidb_enable_fast_analyze=1")
+	tk.MustExec("ANALYZE TABLE t0")
+}
+
+func (s *testSuite1) TestIssue15752(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t0")
+	tk.MustExec("CREATE TABLE t0(c0 INT)")
+	tk.MustExec("INSERT INTO t0 VALUES (0)")
+	tk.MustExec("CREATE INDEX i0 ON t0(c0)")
+	tk.MustExec("set @@tidb_enable_fast_analyze=1")
+	tk.MustExec("ANALYZE TABLE t0 INDEX i0")
+}
+
 func (s *testSuite1) TestAnalyzeIncremental(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
diff --git a/statistics/cmsketch.go b/statistics/cmsketch.go
index d5752ff8527b6..4a40328a28329 100644
--- a/statistics/cmsketch.go
+++ b/statistics/cmsketch.go
@@ -345,7 +345,7 @@ func (c *CMSketch) MergeCMSketch(rc *CMSketch, numTopN uint32) error {
 	if c.depth != rc.depth || c.width != rc.width {
 		return errors.New("Dimensions of Count-Min Sketch should be the same")
 	}
-	if c.topN != nil || rc.topN != nil {
+	if len(c.topN) > 0 || len(rc.topN) > 0 {
 		c.mergeTopN(c.topN, rc.topN, numTopN, false)
 	}
 	c.count += rc.count
@@ -369,7 +369,7 @@ func (c *CMSketch) MergeCMSketch4IncrementalAnalyze(rc *CMSketch, numTopN uint32
 	if c.depth != rc.depth || c.width != rc.width {
 		return errors.New("Dimensions of Count-Min Sketch should be the same")
 	}
-	if c.topN != nil || rc.topN != nil {
+	if len(c.topN) > 0 || len(rc.topN) > 0 {
 		c.mergeTopN(c.topN, rc.topN, numTopN, true)
 	}
 	for i := range c.table {