[doc] Improve the Changelog Generation section of the PrimaryKey Table page (#1189)

Author: ZmmBigdata

website/docs/table-design/table-types/pk-table/index.md

@@ -123,13 +123,33 @@ CREATE TABLE T
 
 If the data written to the primary-key table is
 sequentially `+I(1, 2.0, 'apple')`, `+I(1, 4.0, 'banana')`, `-D(1, 4.0, 'banana')`, then the following change data will
-be generated.
+be generated. For example, the following Flink SQL statements illustrate this behavior:
 
-```text
-+I(1, 2.0, 'apple')
--U(1, 2.0, 'apple')
-+U(1, 4.0, 'banana')
--D(1, 4.0, 'banana')
+```sql title="Flink SQL"
+-- set to batch mode to execute DELETE and INSERT statements
+SET execution.runtime-mode = batch;
+
+-- insert to records with the same primary key k=1
+INSERT INTO T (k, v1) VALUES (1, 2.0,'apple');
+INSERT INTO T (k, v1) VALUES (1, 4.0,'banana');
+
+-- delete the record with primary key k=1
+DELETE FROM T WHERE k = 1;
+
+-- set to streaming mode to observe the changelogs
+SET execution.runtime-mode = streaming;
+SELECT * FROM T;
+```
+
+Generate the following output in the Flink SQL CLI:
+
+```
+| op   | k    | v1   | v2     |
+| ---- | ---- | ---- | ------ |
+| +I   | 1    | 2.0  | apple  |
+| -U   | 1    | 2.0  | apple  |
+| +U   | 1    | 4.0  | banana |
+| -D   | 1    | 4.0  | banana |
 ```
 
 ## Data Queries