SQL Server : unexpected behaviour in while, when using INSERT INTO - sql-server-2008

Question

I guess this is going to be a very easy one for anyone who knows SQL programming...
SQLFiddle
Here is the code I am executing against the database:
DECLARE #maxCounter int
-- Used to get the maximum bound number for my loop, basically what is the highest number of records. Tested, seems to work as expected.
SET #maxCounter = (SELECT TOP 1 COUNT(SN)
FROM TestResults
WHERE Type = 'EX'
GROUP BY SN
ORDER BY COUNT(SN) DESC)
CREATE TABLE #Info
(
DLoc VARCHAR(500),
DCode VARCHAR(500),
Dobs VARCHAR(500)
)
DECLARE #counter INT
SET #counter = 1
WHILE #counter <= #maxCounter
BEGIN
INSERT INTO #Info (DLoc)
VALUES ('Location_' + CAST(#counter AS VARCHAR(16)))
INSERT INTO #Info (DCode)
VALUES ('Code_' + CAST(#counter AS VARCHAR(16)))
INSERT INTO #Info (Dobs)
VALUES ('Observation_' + CAST(#counter AS VARCHAR(16)))
SET #counter = #counter + 1
END
SELECT * FROM #Info;
DROP TABLE #Info;
If you see some weird things in the code, then that is because I am a total beginner and do not know any better.
Expected output of the while loop:
+------------+---------+---------------+
| defLoc | defCode | obs |
+------------+---------+---------------+
| Location_1 | Code_1 | Observation_1 |
| Location_2 | Code_2 | Observation_2 |
| Location_3 | Code_3 | Observation_3 |
+------------+---------+---------------+
Unexpected output result:
defLoc | defCode | obs |
-----------------+-------------+---------------|
Location_1 | | |
| Code_1 | |
| | Observation_1 |
Location_2 | | |
| Code_2 | |
| | Observation_2 |
Location_3 | | |
| Code_3 | |
| | Observation_3 |
I have no clue where the empty cells come from...

Answer 1

You need to use ONE INSERT for each iteration, and specify all three columns and their values in one go:
WHILE #counter <= #maxCounter
BEGIN
INSERT INTO #Info (DLoc, DCode, Dobs)
VALUES ('Location_' + CAST(#counter AS VARCHAR(16)),
'Code_' + CAST(#counter AS VARCHAR(16)),
'Observation_' + CAST(#counter AS VARCHAR(16))
)
SET #counter = #counter + 1
END
Each INSERT will insert a whole row - the value you provided is inserted into the column you specified, but the other columns will all remain NULL.

Answer 2

You can insert each row with 3 different column values with a single insert statement in a loop:
WHILE #counter <= #maxCounter
BEGIN
INSERT INTO #Info (DLoc,DCode,Dobs)
VALUES (
'Location_' + CAST(#counter AS VARCHAR(16))
, 'Code_' + CAST(#counter AS VARCHAR(16))
, 'Observation_' + CAST(#counter AS VARCHAR(16))
);
SET #counter = #counter + 1;
END;
Alternatively, you could insert all rows at once in a single INSERT...SELECT statement using a tally table as the source. If you have no tally table, you can use a CTE to generate the set of numbers. The example below uses a CTE with ROW_NUMBER() that can be extended as needed.
WITH
t10 AS (SELECT n FROM (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) t(n))
,t1k AS (SELECT 0 AS n FROM t10 AS a CROSS JOIN t10 AS b CROSS JOIN t10 AS c)
,t1m AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS num FROM t1k AS a CROSS JOIN t1k AS b CROSS JOIN t1k AS c)
INSERT INTO #Info (DLoc,DCode,Dobs)
SELECT
'Location_' + CAST(num AS VARCHAR(16))
, 'Code_' + CAST(num AS VARCHAR(16))
, 'Observation_' + CAST(num AS VARCHAR(16))
FROM t1m
WHERE num <= #maxCounter;
In SQL Server, set-based operations generally outperform procedural looping constructs by orders of magnitude.