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CREATE TABLE Table1
([Child] int, [Parent] int)
;
INSERT INTO Table1
([Child], [Parent])
VALUES
(1, 2),
(1, 3),
(2, 3)
;
3 rows affected
INSERT INTO table1 (child, parent)
SELECT DISTINCT t1.parent, NULL
FROM table1 t1
LEFT JOIN table1 t2
ON t1.parent = t2.child
WHERE t2.child IS NULL;
1 rows affected
SELECT *
FROM Table1
| Child | Parent |
|---|---|
| 1 | 2 |
| 1 | 3 |
| 2 | 3 |
| 3 | null |