Question

I’m trying to acheive through T-SQL (in a stored procedure) a way to copy a value from a parent into the child when retrieving rows. Here is some example data:

DROP TABLE TEST_LEVELS
CREATE TABLE TEST_LEVELS(
     ID INT NOT NULL
    ,VALUE INT NULL
    ,PARENT_ID INT NULL
    ,LEVEL_NO INT NOT NULL
)

INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (1, 10000, NULL, 1)
INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (2, NULL, 1, 2)
INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (3, NULL, 2, 3)
INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (4, 20000, NULL, 1)
INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (5, NULL, 4, 2)
INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (6, 25000, 5, 3)
INSERT INTO TEST_LEVELS (ID, VALUE, PARENT_ID, LEVEL_NO) VALUES (7, NULL, 6, 4)

Selecting the data as follows:

SELECT ID, VALUE, LEVEL_NO
FROM TEST_LEVELS

results in:

+----+-------+----------+
| ID | VALUE | LEVEL_NO |
+----+-------+----------+
|  1 | 10000 |        1 |
|  2 | NULL  |        2 |
|  3 | NULL  |        3 |
|  4 | 20000 |        1 |
|  5 | NULL  |        2 |
|  6 | 25000 |        3 |
|  7 | NULL  |        4 |
+----+-------+----------+

But I need something like this (values are inherited by the parent):

+----+-------+----------+
| ID | VALUE | LEVEL_NO |
+----+-------+----------+
|  1 | 10000 |        1 |
|  2 | 10000 |        2 |
|  3 | 10000 |        3 |
|  4 | 20000 |        1 |
|  5 | 20000 |        2 |
|  6 | 25000 |        3 |
|  7 | 25000 |        4 |
+----+-------+----------+

Can this be achieved without using cursors (it must also run on SQL Server 2005)?

Answer 1

One way to do it:

SELECT T.ID,
    case when T.VALUE IS NULL
    THEN (SELECT A.VALUE FROM TEST_LEVELS A WHERE A.ID = T.PARENT_ID)
    ELSE T.VALUE
    END,
    T.LEVEL_NO
FROM TEST_LEVELS T