Question

I am testing different foreign key on delete options. I tired cascade, no action, set null, all works, except set default. SQL SERVER just reports error:

Msg 547, Level 16, State 0, Line 1
The DELETE statement conflicted with the FOREIGN KEY constraint “FK_child_parent”. The conflict occurred in database “Test”, table “dbo.Test_parent”, column ‘no’.
The statement has been terminated.

create table Test_parent(
    [no] int primary key    
)

CREATE TABLE test_child(
     SUB1 INT,
    [NO] int DEFAULT 0 CONSTRAINT FK_child_parent REFERENCES Test_parent([no]) ON DELETE set default
)

insert into Test_parent values(1),(2)

insert into test_child values(1, 1)
insert into test_child values(2, 1)

delete from Test_parent

Answer 1

You delete your parent table, which triggers the set default in the child. The DB tries to set the child records to their default 0. But there’s no 0 record in the parent table, triggering the foreign key violation.