CONCAT'ing NULL fields

Question

I have a table with three fields, FirstName, LastName and Email.

Here\'s some dummy data:

FirstName | LastName | Email
Adam        West       adam@west.c         


        

Answer 1

Stefan's answer is correct. To probe a little bit deeper you need to know that NULL is not the same as Nothing. Null represents the absence of a value, or in other words, not defined. Nothing represents an empty string which IS in fact a value.

Undefined + anything = undefined

Good database tidbit to hold onto!

Answer 2

Try

ISNULL(FirstName, '<BlankValue>') -- In SQL Server
IFNULL(Firstname, '<BlankValue>') -- In MySQL

So,

CONCAT(ISNULL(FirstName,''),ISNULL(LastName,''),ISNULL(Email,'')) -- In SQL Server
CONCAT(IFNULL(FirstName,''),IFNULL(LastName,''),IFNULL(Email,'')) -- In MySQL

would return the same thing without the null issue (and a blank string where nulls should be).

Answer 3

In mysql isnull wont work some time. try IFNULL(),

CONCAT(IFNULL(FirstName,''),IFNULL(LastName,''),IFNULL(Email,''))

Answer 4

Starting from MS SQL Server 2012 it was introduced CONCAT function and according to MSDN

Null values are implicitly converted to an empty string. If all the arguments are null, an empty string of type varchar(1) is returned.

so it's enough to use CONCAT without IsNull

CONCAT(FirstName, LastName, Email)

Answer 5

If you get (like I do in MySQL):

#1582 - Incorrect parameter count in the call to native function 'ISNULL'

You can replace ISNULL function by COALESCE:

CONCAT(COALESCE(FirstName,''),COALESCE(LastName,''),COALESCE(Email,''))