on -delete cascade in 1 single table means we delete FK tuples related to PK on that table .
"A foreign key with cascade delete means that if a record in the parent table is deleted, then the corresponding records in the child table will automatically be deleted."~ this is for multiple tables , in case of single table we delete FK tuples which related to deleted PK tuple .
A is PK in this table, A is on-delete cascade.
C is foreign key . We have to maintain Referential Integrity .
tuple (2, 4) is deleted , here 2 is PK , and 2 is in FK in tuples (5,2) and (7,2) so both are deleted .
Now 7 is no where FK . But 5 is FK again in tuple (9,5) hence tuple (9,5) is also deleted .
overall 3 tuples are deleted additionally to preserve referential integrity when the tuple (2, 4) is deleted .