diff --git a/pkg/diff/chunk.go b/pkg/diff/chunk.go
index f51ede381..5731b34dc 100644
--- a/pkg/diff/chunk.go
+++ b/pkg/diff/chunk.go
@@ -281,27 +281,30 @@ func GenerateCheckJob(table *TableInstance, splitField, limits string, chunkSize
 		chunks = chunks[1:]
 
 		args := make([]interface{}, 0, 2)
-		var condition1, condition2 string
+		var (
+			condition1 = "TRUE"
+			condition2 = "TRUE"
+		)
 		if !chunk.noBegin {
+			format := "`%s`%s > ?"
 			if chunk.containBegin {
-				condition1 = fmt.Sprintf("`%s`%s >= ?", column.Name, collation)
-			} else {
-				condition1 = fmt.Sprintf("`%s`%s > ?", column.Name, collation)
+				format = "`%s`%s >= ?"
 			}
+
+			condition1 = fmt.Sprintf(format, column.Name, collation)
 			args = append(args, chunk.begin)
-		} else {
-			condition1 = "TRUE"
 		}
+
 		if !chunk.noEnd {
+			format := "`%s`%s < ?"
 			if chunk.containEnd {
-				condition2 = fmt.Sprintf("`%s`%s <= ?", column.Name, collation)
-			} else {
-				condition2 = fmt.Sprintf("`%s`%s < ?", column.Name, collation)
+				format = "`%s`%s <= ?"
 			}
+
+			condition2 = fmt.Sprintf(format, column.Name, collation)
 			args = append(args, chunk.end)
-		} else {
-			condition2 = "TRUE"
 		}
+
 		where := fmt.Sprintf("(%s AND %s AND %s)", condition1, condition2, limits)
 
 		log.Debugf("%s.%s create dump job, where: %s, begin: %v, end: %v", table.Schema, table.Table, where, chunk.begin, chunk.end)
diff --git a/pkg/diff/diff.go b/pkg/diff/diff.go
index c17bf9d07..b7a4beb09 100644
--- a/pkg/diff/diff.go
+++ b/pkg/diff/diff.go
@@ -506,30 +506,36 @@ func compareData(map1, map2 map[string][]byte, null1, null2 map[string]bool, ord
 			return false, 0, errors.Errorf("don't have key %s", col.Name.O)
 		}
 		if needQuotes(col.FieldType) {
-			if string(data1) > string(data2) {
-				cmp = 1
-				break
-			} else if string(data1) < string(data2) {
-				cmp = -1
-				break
-			} else {
+
+			strData1 := string(data1)
+			strData2 := string(data2)
+
+			if len(strData1) == len(strData2) && strData1 == strData2 {
 				continue
 			}
+
+			cmp = -1
+			if strData1 > strData2 {
+				cmp = 1
+			}
+			break
+
 		} else {
 			num1, err1 := strconv.ParseFloat(string(data1), 64)
 			num2, err2 := strconv.ParseFloat(string(data2), 64)
 			if err1 != nil || err2 != nil {
 				return false, 0, errors.Errorf("convert %s, %s to float failed, err1: %v, err2: %v", string(data1), string(data2), err1, err2)
 			}
+
+			if num1 == num2 {
+				continue
+			}
+
+			cmp = -1
 			if num1 > num2 {
 				cmp = 1
-				break
-			} else if num1 < num2 {
-				cmp = -1
-				break
-			} else {
-				continue
 			}
+			break
 		}
 	}
 
diff --git a/pkg/diff/merge.go b/pkg/diff/merge.go
index 610ec8656..7e4894f1c 100644
--- a/pkg/diff/merge.go
+++ b/pkg/diff/merge.go
@@ -41,11 +41,10 @@ func (r RowDatas) Less(i, j int) bool {
 		data1 = r.Rows[i].Data[col.Name.O]
 		data2 = r.Rows[j].Data[col.Name.O]
 		if needQuotes(col.FieldType) {
-			if string(data1) > string(data2) {
-				return false
-			} else if string(data1) < string(data2) {
-				return true
-			} else {
+			strData1 := string(data1)
+			strData2 := string(data2)
+
+			if strData1 == strData2 {
 				// `NULL` is less than ""
 				if r.Rows[i].Null[col.Name.O] {
 					return true
@@ -55,20 +54,25 @@ func (r RowDatas) Less(i, j int) bool {
 				}
 				continue
 			}
-		} else {
-			num1, err1 := strconv.ParseFloat(string(data1), 64)
-			num2, err2 := strconv.ParseFloat(string(data2), 64)
-			if err1 != nil || err2 != nil {
-				log.Fatalf("convert %s, %s to float failed, err1: %v, err2: %v", string(data1), string(data2), err1, err2)
-			}
-			if num1 > num2 {
+			if strData1 > strData2 {
 				return false
-			} else if num1 < num2 {
-				return true
-			} else {
-				continue
 			}
+			return true
+		}
+		num1, err1 := strconv.ParseFloat(string(data1), 64)
+		num2, err2 := strconv.ParseFloat(string(data2), 64)
+		if err1 != nil || err2 != nil {
+			log.Fatalf("convert %s, %s to float failed, err1: %v, err2: %v", string(data1), string(data2), err1, err2)
 		}
+
+		if num1 == num2 {
+			continue
+		}
+		if num1 > num2 {
+			return false
+		}
+		return true
+
 	}
 
 	return true