Trigger for table synchronization update problems

1 SQL server 2000 trigger, table synchronization update problem
2. There are three tables, A, B, and C.
Table 3A and Table B contain three fields: A1, B1, and C1,
Set A1, B1, and C1 in Table A and Table B in table 4C,
5. All fields are nvarchar (10 ),
6. Data in Table A should be updated, deleted, and inserted to Table C.
7. Data in Table B should be updated, deleted, and inserted to Table C.
8 assume that there is A unique index on a1, b1, and c1 in Table A and Table B.
    9
10
11 This problem can be easily solved theoretically, because we can see from the requirements that the data stored in Table C is essentially the union of tables A and B. You can create the same trigger on Table A and Table B. Once Table A and Table B change, such as insert, delete, or update, the data in Table C can be cleared, then insert the union data in Table A and Table B into table C to achieve the goal: haha...
12
13 the following trigger implementation principle is:
14
15 when table A inserts data, check whether Table C contains the data to be inserted in Table A. If not, insert this row into table C. Otherwise, no operation is required.
16
17 When Table A is updated, check whether the row of data before update exists in Table B. If yes, this row of data should be retained in Table C and the updated data in Table A should be inserted into table C. If Table B does not have this row of data before Table A's update and Table C does not have this row of data after table A's update, you need to use the updated data of Table A to update the data of the same row in Table C as that of Table A before the update; if Table B does not have this row of data updated in Table A and Table C has this row of data updated in Table, you need to delete the row data that is the same as that of Table A before update from Table C (because after table A is updated, neither table A nor Table B has the row data before Table A is updated, this row of data should not exist in Table C ).
18
19 when Table A is deleted, check whether Table B still has this row of data to be deleted. If yes, the same row of data in Table C and table A cannot be deleted. Otherwise, delete the instance.
20
21
22. The trigger principle in Table B is the same as that in Table.
23
24
25 create trigger SYNC_C_BY_A
26ON
27 after insert, UPDATE, DELETE
28AS
29 Declare @ Dml TinyInt --