T-SQL: Conditional NULL removal - sql

Question

I need to select only the Room_IDs that have no instances where the Status is NULL.
For example here :
TABLE_A
Room_Id Status Inspection_Date
-----------------------------------
1 NULL 5/15/2015
2 occupied 5/21/2015
2 NULL 1/19/2016
1 occupied 12/16/2015
4 NULL 3/25/2016
3 vacant 8/27/2015
1 vacant 4/17/2016
3 vacant 12/12/2015
3 vacant 3/22/2016
4 vacant 2/2/2015
4 vacant 3/24/2015
My result should look like this:
Room_Id Status Inspection_Date
-----------------------------------
3 vacant 8/27/2015
3 vacant 12/12/2015
3 vacant 3/22/2016
Because Room_ID '3' has no instances where the Status is NULL

Answer 1

Quick example of how to do it:
DECLARE #tTable TABLE(
Room_Id INT,
Status VARCHAR(20),
Inspection_Date DATETIME)
INSERT INTO #tTable VALUES
(1, NULL, '5/15/2015'),
(1,NULL, '5/15/2015'),
(2,'occupied', '5/21/2015'),
(2,NULL, '1/19/2016'),
(1,'occupied', '12/16/2015'),
(4,NULL, '3/25/2016'),
(3,'vacant', '8/27/2015'),
(1,'vacant', '4/17/2016'),
(3,'vacant', '12/12/2015'),
(3,'vacant', '3/22/2016'),
(4,'vacant', '2/2/2015'),
(4,'vacant', '3/24/2015')
SELECT * FROM #tTable T1
WHERE Room_Id NOT IN (SELECT Room_ID FROM #tTable WHERE Status IS NULL)
Gives :
Room_Id | Status | Inspection_Date |
-------------------------------------------------
3 | vacant | 2015-08-27 00:00:00.000
3 | vacant | 2015-12-12 00:00:00.000
3 | vacant | 2016-03-22 00:00:00.000

Answer 2

Try this out:
SELECT *
FROM Table1
WHERE Room_ID NOT IN
(
SELECT DISTINCT Room_ID
FROM Table1
WHERE Status IS NULL
)
The sub query returns a list of unique room id's that, at one time or another, had a NULL status. The outer query looks at that list, and says "Return * where the room_ID IS NOT one those in the subquery.
If you want to try it in SQL Fiddle, here is the Schema:
CREATE TABLE Table1
(Room_ID int, Status varchar(8), Inspection_Date datetime)
;
INSERT INTO Table1
(Room_ID, Status, Inspection_Date)
VALUES
(1, NULL, '2015-05-15 00:00:00'),
(2, 'occupied', '2015-05-21 00:00:00'),
(2, NULL, '2016-01-19 00:00:00'),
(1, 'occupied', '2015-12-16 00:00:00'),
(4, NULL, '2016-03-25 00:00:00'),
(4, 'vacant', '2015-08-27 00:00:00'),
(1, 'vacant', '2016-04-17 00:00:00'),
(3, 'vacant', '2015-12-12 00:00:00'),
(3, 'vacant', '2016-03-22 00:00:00'),
(4, 'vacant', '2015-02-02 00:00:00'),
(4, 'vacant', '2015-03-24 00:00:00'),
(2, NULL, '2015-05-22 00:00:00')
;

Answer 3

As alternative to Hashman, I just prefer to use not exists over not in for these types of queries.
Creating some test data
Note that I just kept the same date for everything since it's not imperative to the question.
create table #table_a (
Room_Id int,
Status varchar(32),
Inspection_Date date);
insert #table_a (Room_Id, Status, Inspection_Date)
values
(1, null, getdate()),
(2, 'occupied', getdate()),
(2, null, getdate()),
(1, 'occupied', getdate()),
(4, null, getdate()),
(3, 'vacant', getdate()),
(1, 'vacant', getdate()),
(3, 'vacant', getdate()),
(3, 'vacant', getdate()),
(4, 'vacant', getdate()),
(4, 'vacant', getdate());
The query
select *
from #table_a t1
where not exists (
select *
from #table_a t2
where t1.Room_Id = t2.Room_Id
and Status is null);
The results
Room_Id Status Inspection_Date
----------- -------------------------------- ---------------
3 vacant 2016-06-17
3 vacant 2016-06-17
3 vacant 2016-06-17

Answer 4

You can use CTE and NOT EXIST like below code
WITH bt
AS ( SELECT RoomId ,
Status,
Inspection_Date
FROM dbo.Table_1
)
SELECT *
FROM bt AS a
WHERE NOT EXISTS ( SELECT 1
FROM bt
WHERE bt.RoomId = a.RoomId
AND bt.Status IS NULL );