SQL Server String Concatenation with Null - sql-server

Question

I am creating a computed column across fields of which some are potentially null.
The problem is that if any of those fields is null, the entire computed column will be null. I understand from the Microsoft documentation that this is expected and can be turned off via the setting SET CONCAT_NULL_YIELDS_NULL. However, there I don't want to change this default behavior because I don't know its implications on other parts of SQL Server.
Is there a way for me to just check if a column is null and only append its contents within the computed column formula if its not null?

Answer 1

You can use ISNULL(....)
SET #Concatenated = ISNULL(#Column1, '') + ISNULL(#Column2, '')
If the value of the column/expression is indeed NULL, then the second value specified (here: empty string) will be used instead.

Answer 2

From SQL Server 2012 this is all much easier with the CONCAT function.
It treats NULL as empty string
DECLARE #Column1 VARCHAR(50) = 'Foo',
#Column2 VARCHAR(50) = NULL,
#Column3 VARCHAR(50) = 'Bar';
SELECT CONCAT(#Column1,#Column2,#Column3); /*Returns FooBar*/

Answer 3

Use COALESCE. Instead of your_column use COALESCE(your_column, ''). This will return the empty string instead of NULL.

Answer 4

You can also use CASE - my code below checks for both null values and empty strings, and adds a seperator only if there is a value to follow:
SELECT OrganisationName,
'Address' =
CASE WHEN Addr1 IS NULL OR Addr1 = '' THEN '' ELSE Addr1 END +
CASE WHEN Addr2 IS NULL OR Addr2 = '' THEN '' ELSE ', ' + Addr2 END +
CASE WHEN Addr3 IS NULL OR Addr3 = '' THEN '' ELSE ', ' + Addr3 END +
CASE WHEN County IS NULL OR County = '' THEN '' ELSE ', ' + County END
FROM Organisations

Answer 5

Use
SET CONCAT_NULL_YIELDS_NULL OFF
and concatenation of null values to a string will not result in null.
Please note that this is a deprecated option, avoid using.
See the documentation for more details.

Answer 6

I just wanted to contribute this should someone be looking for help with adding separators between the strings, depending on whether a field is NULL or not.
So in the example of creating a one line address from separate fields
Address1, Address2, Address3, City, PostCode
in my case, I have the following Calculated Column which seems to be working as I want it:
case
when [Address1] IS NOT NULL
then ((( [Address1] +
isnull(', '+[Address2],'')) +
isnull(', '+[Address3],'')) +
isnull(', '+[City] ,'')) +
isnull(', '+[PostCode],'')
end
Hope that helps someone!

Answer 7

ISNULL(ColumnName, '')

Answer 8

I had a lot of trouble with this too. Couldn't get it working using the case examples above, but this does the job for me:
Replace(rtrim(ltrim(ISNULL(Flat_no, '') +
' ' + ISNULL(House_no, '') +
' ' + ISNULL(Street, '') +
' ' + ISNULL(Town, '') +
' ' + ISNULL(City, ''))),' ',' ')
Replace corrects the double spaces caused by concatenating single spaces with nothing between them. r/ltrim gets rid of any spaces at the ends.

Answer 9

In Sql Server:
insert into Table_Name(PersonName,PersonEmail) values(NULL,'xyz#xyz.com')
PersonName is varchar(50), NULL is not a string, because we are not passing with in single codes, so it treat as NULL.
Code Behind:
string name = (txtName.Text=="")? NULL : "'"+ txtName.Text +"'";
string email = txtEmail.Text;
insert into Table_Name(PersonName,PersonEmail) values(name,'"+email+"')

Answer 10

This example will help you to handle various types while creating insert statements
select
'insert into doc(Id, CDate, Str, Code, Price, Tag )' +
'values(' +
'''' + convert(nvarchar(50), Id) + ''',' -- uniqueidentifier
+ '''' + LEFT(CONVERT(VARCHAR, CDate, 120), 10) + ''',' -- date
+ '''' + Str+ ''',' -- string
+ '''' + convert(nvarchar(50), Code) + ''',' -- int
+ convert(nvarchar(50), Price) + ',' -- decimal
+ '''' + ISNULL(Tag, '''''') + '''' + ')' -- nullable string
from doc
where CDate> '2019-01-01 00:00:00.000'