Check and Change for empty or null value of column in SQL? - sql

Question

How can I change column text Not Exists when it is empty or null ?
My query :
Select TOP 1 ISNULL(NULLIF(DR.Name,''),'Not Exists') as Name,
DR.Name as Name ,Coalesce(NullIf(rtrim(DR.Name),''),'Not Exist') as Name,
Name = case when DR.Name is null then 'Not Exists'
when DR.Name='' then 'Not Exists' else DR.Name end
from Transfer TR
join Driver DR on DR.OID=TR.DriverID
WHERE TR.TruckID=51 AND TR.Statues<>7 and TR.DateScheduled<GETDATE()
AND TR.DateScheduled>=DATEADD(DAY,-7,GETDATE()) ORDER BY TR.OID DESC
Result :

Answer 1

If you just need a single column, then you can use a sub-select, this way when no rows are returned by the query you will still get not exists:
SELECT Name = ISNULL(( SELECT TOP 1 NULLIF(DR.Name,'')
FROM Transfer AS TR
INNER JOIN Driver AS DR
ON DR.OID = TR.DriverID
WHERE TR.TruckID = 51
AND TR.Statues <> 7
AND TR.DateScheduled < GETDATE()
AND TR.DateScheduled >= DATEADD(DAY, -7, GETDATE())
ORDER BY TR.OID DESC), 'Not Exists');
If you need multiple columns then you could union your Not Exists record to the bottom of the query, place all this inside a subquery then select the top 1 again, ensuring that your actual value takes precedence (by adding the column SortOrder):
SELECT TOP 1 Name, SomeOtherColumn
FROM ( SELECT TOP 1
Name = NULLIF(DR.Name,''),
SomeOtherColumn,
SortOrder = 0
FROM Transfer AS TR
INNER JOIN Driver AS DR
ON DR.OID = TR.DriverID
WHERE TR.TruckID = 51
AND TR.Statues <> 7
AND TR.DateScheduled < GETDATE()
AND TR.DateScheduled >= DATEADD(DAY, -7, GETDATE())
ORDER BY TR.OID DESC
UNION ALL
SELECT 'Not Exists', NULL, 1
) AS t
ORDER BY SortOrder;

Answer 2

I'm not entirely sure I understand your question, but if you are trying to catch nulls and empty strings "in one go", try this:
select TOP 1
case when length(trim(coalesce(DR.Name, ''))) = 0 then
'Not Exists'
else
DR.Name
as Name
....
The coalesce catches the NULLs and sets a replacement value. The trim gets rid of any padding and the length checks if what is left is an empty string --> so this covers nulls, padded- and non-padded trivial strings.

Answer 3

Assuming the value has regular spaces, the following would keep your approach:
Select TOP 1 ISNULL(NULLIF(ltrim(rtrim((DR.Name))), ''), 'Not Exists') as Name,
I would probably go with the more explicit:
select top 1 (case when ltrim(rtrim((DR.Name)) = '' or DR.Name is null then 'Not Exists'
else DR.Name end) as Name
Unless you also wanted the spaces removed from Name in the output.
If you have other characters, then you can use ASCII() to find them. Something like:
select ASCII(LEFT(DR.Name, 1))
. . .
where LEFT(DR.Name, 1) NOT LIKE '[a-zA-Z0-9 ]' -- you can expand this list of allowed characters

Answer 4

It seems to me you are not actually looking for a way to replace an empty string with 'Not Exists', but an empty result set.
In other words: It looks like you are looking for a way to show 'Not Exists' in case your query returns no rows. If it is this what you are looking for, then first "add" a 'Not Exists' record to your result set and then show the best row, i.e. the desired row in case such a row exists, else your 'Not Exists' row.
select top 1 name
from
(
select name, tr.oid
from transfer tr
join driver dr on dr.oid=tr.driverid
where tr.truckid=51 and tr.statues<>7 and tr.datescheduled<getdate()
and tr.datescheduled>=dateadd(day,-7,getdate())
union all
select 'Not Exists', -1
)
order by oid desc;
I chose -1 for the dummy OID. It must be a value smaller than any real OID. So if you have negative values, make that value even smaller.