#gate cs applied course

Question

Answer 1

In all three scripts, the first step is to delete rows from table C. This is because table C does not have any foreign key constraints that would prevent it from being deleted.

After that, the order of the remaining delete statements depends on the foreign key constraints in the tables. In script I, the next step is to delete rows from table B. This is because table B has a foreign key constraint that references table A, and the on delete set NULL clause means that the rows in table B that reference rows that are deleted from table A will have their foreign key values set to NULL.

In script II, the next step is to delete rows from table D. This is because table D has two foreign key constraints, one that references table B and one that references table A. The on delete set NULL clause in the constraint that references table B means that the rows in table D that reference rows that are deleted from table B will have their foreign key values set to NULL, and the on update cascade clause in the constraint that references table A means that any changes to the primary key values in table A will be automatically propagated to the rows in table D that reference those values.

In script III, the next step is to delete rows from table D. This is because table D has two foreign key constraints, one that references table B and one that references table A. The on delete set NULL clause in the constraint that references table B means that the rows in table D that reference rows that are deleted from table B will have their foreign key values set to NULL.

Finally, in all three scripts, the last step is to delete rows from table A. This is because all of the other tables have foreign key constraints that reference table A, and the on delete set NULL and on update cascade clauses in those constraints mean that the rows in those tables that reference table A will either be set to NULL or updated automatically when rows are deleted from table A.

Answer 2

Let's analyze the dependencies between the tables:

Table A has no dependencies on other tables and is referenced by tables B, C, and D.
Table B depends on table A and is referenced by table D.
Table C depends on table A and is not referenced by any other table.
Table D depends on tables A and B and is not referenced by any other table.
Based on these dependencies, you should delete the records from the tables in the reverse order of their dependencies to avoid violating any foreign key constraints.

So, the correct order to delete records from all tables without causing an error would be:

Delete from C
Delete from D
Delete from B
Delete from A