SQL Server: Recursive table update - sql-server

Question

I have a table, let's say TestTable. This table has below columns:
ID1 | ID2 | ID3 | LEVEL | PARENT_LEVEL | ENABLED | OBSOLET
All columns are integers, ENABLED and OBSOLET only two possible values (0 or 1)
LEVEL Column can have a parent level, thi parent level another parent level and so on, for example, imagine following table content:
ID1 | ID2 | ID3 | LEVEL | PARENT_LEVEL | ENABLED | OBSOLET
1 6 7 98 NULL 1 0
1 6 6 99 98 1 0
1 4 6 100 99 1 0
1 2 3 200 100 1 0
2 4 1 300 NULL 0 0
3 3 4 400 NULL 0 1
3 4 5 500 400 0 0
ID1, ID2 and ID3 is the primary key.
So representing this in a tree:
+ 98
|__ 99
|__ 100
|___ 200
+ 300
+ 400
|__ 500
200 has 100 as parent, 100 has 99 as parent and 99 has 98 as parent.
300 has no parent.
500 has 400 as parent and 400 has no parent.
So what I need is an update query to update recursively the field 'ENABLED', for example:
If I update LEVEL 99 with ENABLED=1, also his parent, 98 must be updated to ENABLED=1 but not LEVELs 100 and 200.
If I update LEVEL 200 with ENABLED=1, also his parent, 100 must be updated with ENABLED=1, and also LEVELs 99 and 98, because they have parents as well.
If I update LEVEL 300 with ENABLED=1, only LEVEL 300 is updated because it has no parent.
So I need a recursive update query to update field ENABLED until LEVEL has no parent (PARENT_LEVEL). Also I need to update all the levels at once with one update query, not only execute update for a concret level.
Furthermore, on each update I need to check field 'OBSOLET', and if a LEVEL has field OBSOLET set to 1 it means that rollback has to be made, for example, taken into account above table content, if I update LEVEL 500 to ENABLED=1, no problem because its OBSOLET field is 0, so its field ENABLED is set to 1, then by recursive, we try to update its parent, LEVEL 400, to ENABLED=1, but as its OBSOLET field is set to 1 it means rollback needs to be made, that is, ENABLED field for LEVEL 400 is kept to 0 (not updated) and field ENABLED for level 500 that was set to 1 should be reverted to 0 as well.
The final problem is that this update query should be within a trigger on this table TestTable:
CREATE TRIGGER [dbo].[TG_TestTable]
ON [dbo].[TestTable]
FOR UPDATE
AS
IF UPDATE ([ENABLED])
BEGIN
// Update query must be here, so if field ENABLED is updated, trigger is fired again...so I don't know if disable trigger statement is necessary to be done before this update query and enable trigger after it.
END
This is because to activate the trigger, an update is performed on some rows of the table TestTable, for example:
UPDATE [dbo].[TestTable]
SET ENABLED = 1
WHERE
LEVEL IN (100,300,500);
so I have tried to make the update query within the trigger but I do not know how to finish it:
UPDATE [dbo].[TestTable]
SET ENABLED= inserted.ENABLED
..... // SOMETHING ELSE
FROM inserted
WHERE
[dbo].[TestTable].ID1 = inserted.ID1
AND
[dbo].[TestTable].ID2 = inserted.ID2
AND
[dbo].[TestTable].ID3 = inserted.ID3
AND
[dbo].[TestTable].PARENT_LEVEL = inserted.LEVEL;
So how can I achieve this? maybe using a recursive function or recursive CTE? or is better a recursive trigger on same table in terms of time execution and performance? All ideas will be welcome.

Answer 1

I've found a solution for this. It's quite a long one, but it's fairly easy to understand.
First, Create and populate sample table (Please save us this step in your future questions)
CREATE TABLE TestTable
(
ID1 int NOT NULL,
ID2 int NOT NULL,
ID3 int NOT NULL,
LEVEL int NOT NULL,
PARENT_LEVEL int,
ENABLED int,
OBSOLET int,
PRIMARY KEY (ID1, ID2, ID3)
)
INSERT INTO TestTable VALUES
(1, 6, 7, 98, NULL, 1, 0),
(1, 6, 6, 99, 98 , 0, 0),
(1, 4, 6, 100, 99 , 0, 0),
(1, 2, 3, 200, 100 , 0, 0),
(2, 4, 1, 300, NULL, 0, 0),
(3, 3, 4, 400, NULL, 0, 1),
(3, 4, 5, 500, 400 , 0, 0)
Then, Create an INSTEAD OF UPDATE trigger, that will only update the records matching your criteria.
Note: This will also update records where the enabled value was not changed, You'll see it in the code soon.
Answer code
CREATE TRIGGER tr_TestTable_IOU ON TestTable
INSTEAD OF UPDATE
AS
;WITH CTE AS
( -- A recursive cte to get all the parents of the updated records
SELECT i.ID1,
i.ID2,
i.ID3,
i.LEVEL,
i.PARENT_LEVEL,
i.ENABLED,
i.OBSOLET
FROM inserted i
INNER JOIN deleted d ON i.ID1 = d.ID1
AND i.ID2 = d.ID2
AND i.ID3 = d.ID3
WHERE i.ENABLED = 1
AND d.ENABLED = 0
-- The where clause will allow only records where enabled was changed from 0 to 1
UNION ALL
SELECT t.ID1,
t.ID2,
t.ID3,
t.LEVEL,
t.PARENT_LEVEL,
t.ENABLED,
t.OBSOLET
FROM TestTable t
INNER JOIN CTE ON t.LEVEL = CTE.PARENT_LEVEL
), CTE_OBSOLET AS
( -- A second recursive cte to get all the records where at least in one parent the value of OBSOLET = 1
SELECT i.ID1,
i.ID2,
i.ID3,
i.LEVEL,
i.PARENT_LEVEL,
i.ENABLED,
i.OBSOLET
FROM TestTable i
WHERE OBSOLET = 1
UNION ALL
SELECT t.ID1,
t.ID2,
t.ID3,
t.LEVEL,
t.PARENT_LEVEL,
t.ENABLED,
1
FROM TestTable t
INNER JOIN CTE_OBSOLET ON t.PARENT_LEVEL = CTE_OBSOLET.LEVEL
)
-- Update the enabled column to all relevant records (including parents)
UPDATE t
SET ENABLED = 1
FROM TestTable t
INNER JOIN CTE ON t.ID1 = CTE.ID1
AND t.ID2 = CTE.ID2
AND t.ID3 = CTE.ID3
LEFT JOIN CTE_OBSOLET ON t.ID1 = CTE_OBSOLET.ID1
AND t.ID2 = CTE_OBSOLET.ID2
AND t.ID3 = CTE_OBSOLET.ID3
WHERE CTE_OBSOLET.LEVEL IS NULL -- Assuming the LEVEL is not nullable. Any other not nullable column can be used here
-- Update records where columns other then ENABLED was changed.
-- Since this is an instead of update trigger, you have to include this to enable updates on other columns.
-- This assumes that you can't update the columns of the primary key (ID1, ID2 and ID3).
UPDATE t
SET LEVEL = i.LEVEL,
PARENT_LEVEL = i.PARENT_LEVEL,
OBSOLET = i.OBSOLET
FROM TestTable t
INNER JOIN inserted i ON t.ID1 = i.ID1
AND t.ID2 = i.ID2
AND t.ID3 = i.ID3
INNER JOIN deleted d ON i.ID1 = d.ID1
AND i.ID2 = d.ID2
AND i.ID3 = d.ID3
WHERE i.LEVEL <> d.LEVEL
OR d.PARENT_LEVEL <> i.PARENT_LEVEL
OR d.OBSOLET <> i.OBSOLET
GO
Testing:
SELECT *
FROM TestTable
Results:
ID1 ID2 ID3 LEVEL PARENT_LEVEL ENABLED OBSOLET
1 6 7 98 NULL 1 0
1 6 6 99 98 0 0
1 4 6 100 99 0 0
1 2 3 200 100 0 0
2 4 1 300 NULL 0 0
3 3 4 400 NULL 0 1
3 4 5 500 400 0 0
Do a couple of updates:
UPDATE TestTable
SET ENABLED = 1
WHERE LEVEL IN(200, 500)
UPDATE TestTable
SET ENABLED = 1,
OBSOLET = 1
WHERE LEVEL = 500
Test results:
SELECT *
FROM TestTable
Results:
ID1 ID2 ID3 LEVEL PARENT_LEVEL ENABLED OBSOLET
1 6 7 98 NULL 1 0
1 6 6 99 98 1 0
1 4 6 100 99 1 0
1 2 3 200 100 1 0
2 4 1 300 NULL 0 0
3 3 4 400 NULL 0 1
3 4 5 500 400 0 1