[doc]The deletion operation requires the equivalence condition of the primary key

Author: ZmmBigdata

website/docs/table-design/table-types/pk-table/merge-engines/default.md

@@ -54,7 +54,7 @@ SELECT * FROM T WHERE k = 1;
 
 -- Update
 INSERT INTO T(k, v1, v2) VALUES (2, 2.0, 't2');
--- Switch to batch mode to perform update operation, otherwise an error will be reported: org.apache.flink.table.api.TableException: UPDATE statement is not supported for streaming mode now.
+-- Switch to batch mode to perform update operation for UPDATE statement is only supported for batch mode currently
 SET execution.runtime-mode = batch;
 UPDATE T SET v1 = 4.0 WHERE k = 2;
 SELECT * FROM T WHERE k = 2;
@@ -86,11 +86,13 @@ SELECT * FROM T WHERE k = 3;
 
 -- Delete
 DELETE FROM T WHERE k = 2;
-SELECT * FROM T WHERE k = 2;
+-- Switch to streaming mode
+SET execution.runtime-mode = streaming;
+SELECT * FROM T;
 -- Output:
-+----+-----+------+
-| k  | v1  | v2   |
-+----+-----+------+
-|null| null| null |
-+----+-----+------+
++----+-----+----+
+| k  | v1  | v2 |
++----+-----+----+
+| 1  | 1.0 | t2 |
++----+-----+----+
 ```