*: check delete unique key's handle to handle corner case (#52975) (#…

…53701)

close #52914

table/tables/index.go

@@ -340,9 +340,28 @@ func (c *index) Delete(sc *stmtctx.StatementContext, txn kv.Transaction, indexed
 
 	if distinct {
 		if len(key) > 0 {
-			err = txn.GetMemBuffer().DeleteWithFlags(key, kv.SetNeedLocked)
-			if err != nil {
-				return err
+			okToDelete := true
+			if c.idxInfo.BackfillState != model.BackfillStateInapplicable {
+				// #52914: the delete key is covered by the new ingested key, which shouldn't be deleted.
+				originVal, err := getKeyInTxn(context.TODO(), txn, key)
+				if err != nil {
+					return err
+				}
+				if len(originVal) > 0 {
+					oh, err := tablecodec.DecodeHandleInUniqueIndexValue(originVal, c.tblInfo.IsCommonHandle)
+					if err != nil {
+						return err
+					}
+					if !h.Equal(oh) {
+						okToDelete = false
+					}
+				}
+			}
+			if okToDelete {
+				err = txn.GetMemBuffer().DeleteWithFlags(key, kv.SetNeedLocked)
+				if err != nil {
+					return err
+				}
 			}
 		}
 		if len(tempKey) > 0 {