IF Else string check condition in sql server - sql

Question

I have a records like below :
Name Count
123456M2.txt NULL
123456M2.txt 15
123456M.txt NULL
First record shoud show me NULL, as there is a number after "M" letter in name and Count < 0
Second record shoud show me 1, and there is a number after "M" letter in name and Count > 0
Third record should show me "some number from another field" as, there is no number after "M" letter in name.
Can you guide me on how to write this query.
I am able to do CASE - WHEN query, but not able to proceed with IF ELSE condition of letter check
CASE
WHEN CHARINDEX('M', [FILE_NAME]) > 0 THEN 'COUNT'

Answer 1

You need to use multiple conditions for each WHEN in the CASE:
(psuedocode)
WHEN {Name contains 'M'} AND {character after 'M' is a number} AND {Count is NULL or < 0} THEN NULL
WHEN {Name contains 'M'} AND {character after 'M' is a number} AND {Count is NULL or < 0} THEN 1
etc...
there is no need to try to add IF..ELSE logic anywhere in your query.

Answer 2

I would phrase this as:
select . . .,
(case when name like '%M[0-9]%' and count > 0 then 1
when name like '%M[0-9]%' then 0
else "some number from another field"
end)
A case expression evaluates the conditions in order, stopping at the first one that evaluates to "true".
Your description is a bit unclear, because NULL is not < 0.

Answer 3

Try the following
DECLARE #TBL TABLE (Name VARCHAR(25), [Count] INT);
INSERT INTO #TBL VALUES
('123456M2.txt', NULL),
('123456M2.txt', 15),
('123456M.txt', NULL);
SELECT *,
CASE WHEN Name LIKE '%M[0-9]%' AND ([Count] IS NULL OR [Count] < 0) THEN --Check for NULL too cause NULL is not < 0
NULL
WHEN Name LIKE '%M[0-9]%' AND [Count] > 0 THEN
1
WHEN Name LIKE '%M.%' THEN
555 --Other value from other column
END AS Results
FROM #TBL;
Results:
+--------------+-------+---------+
| Name | Count | Results |
+--------------+-------+---------+
| 123456M2.txt | | |
| 123456M2.txt | 15 | 1 |
| 123456M.txt | | 555 |
+--------------+-------+---------+