SQL Server 2016

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CREATE TABLE a (aid INT PRIMARY KEY);
INSERT INTO a (aid)
VALUES (1), (2), (3) ;
3 rows affected

CREATE TABLE b 
( aid INT,
  bid INT PRIMARY KEY,
  CONSTRAINT [My_FORIEGN_KEY]
    FOREIGN KEY (aid) REFERENCES a (aid)
) ;
INSERT INTO b (aid, bid)
VALUES
  (1, 11),
  (1, 12),
  (2, 21), 
  (3, 31) ;
4 rows affected

INSERT INTO b (aid, bid)
VALUES
  (6, 61),
  (6, 62) ;
Msg 547 Level 16 State 0 Line 1
The INSERT statement conflicted with the FOREIGN KEY constraint "My_FORIEGN_KEY". The conflict occurred in database "fiddle_e8ed92f3152e49d3b29370ac273a56fe", table "dbo.a", column 'aid'.
Msg 3621 Level 0 State 0 Line 1
The statement has been terminated.

SELECT * FROM b ;


aid
bid


1
11

1
12

2
21

3
31


ALTER TABLE b NOCHECK CONSTRAINT [My_FORIEGN_KEY];   --disable
INSERT INTO b (aid, bid)
VALUES
  (4, 41),
  (4, 42) ;
2 rows affected

SELECT * FROM b ;


aid
bid


1
11

1
12

2
21

3
31

4
41

4
42


ALTER TABLE b WITH NOCHECK CHECK CONSTRAINT [My_FORIEGN_KEY];  -- enable constraint without checking
SELECT * FROM b ;


aid
bid


1
11

1
12

2
21

3
31

4
41

4
42


INSERT INTO b (aid, bid)
VALUES
  (6, 61),
  (6, 62) ;
Msg 547 Level 16 State 0 Line 1
The INSERT statement conflicted with the FOREIGN KEY constraint "My_FORIEGN_KEY". The conflict occurred in database "fiddle_e8ed92f3152e49d3b29370ac273a56fe", table "dbo.a", column 'aid'.
Msg 3621 Level 0 State 0 Line 1
The statement has been terminated.

SELECT * FROM b ;


aid
bid


1
11

1
12

2
21

3
31

4
41

4
42


ALTER TABLE b WITH CHECK CHECK CONSTRAINT [My_FORIEGN_KEY];  -- enable constraint and check
Msg 547 Level 16 State 0 Line 1
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "My_FORIEGN_KEY". The conflict occurred in database "fiddle_e8ed92f3152e49d3b29370ac273a56fe", table "dbo.a", column 'aid'.