Question

I have a multiple fields that needs to be put into a string only when there is something in the field and on top of that I don’t want the commas between fields if they are null. I tried using case when but am clearly doing something wrong and would appreciate some help with the following:

USE newCityCollection

UPDATE PropertyInformationDump
SET    RegistryAdd = (CASE
                        WHEN b.OCAREOF IS NULL THEN Isnull(b.OCAREOF, '')
                        ELSE b.OCAREOF + ' ,'
                      END) + (CASE
                                WHEN b.O1STADD IS NULL THEN Isnull(b.O1STADD, '')
                                ELSE b.O1STADD + ' ,'
                              END) + (CASE
                                        WHEN b.O2NDADD IS NULL THEN Isnull(b.O2NDADD, '')
                                        ELSE b.O2NDADD + ' ,'
                                      END) + (CASE
                                                WHEN b.OSTNAME IS NULL THEN Isnull(b.OSTNAME, '')
                                                ELSE b.OSTNAME + ' ,'
                                              END) + (CASE
                                                        WHEN b.OCITYST IS NULL THEN Isnull(b.OCITYST, '')
                                                        ELSE b.OCITYST + ' ,'
                                                      END) + (CASE
                                                                WHEN b.OZIP IS NULL THEN Isnull(b.OZIP, '')
                                                                ELSE b.OZIP + ' ,'
                                                              END)
FROM   dbo.vw_BRT b
WHERE  BRTNumber = b.PARCEL

When I execute that on a field I get nada and am not sure why which is likely a fundemental misunderstanding of how CASE works. I did make sure those fields were actually null and not empty so that is not the problem.

Answer 1

Consider the following: when you join strings together in SQL, and one of them is null, the result is null(*). So, if you add the comma before eliminating nulls, it’s a tad easier:

SELECT COALESCE(b.OCAREOF + ' ,','') + COALESCE(b.O1STADD + ' ,','') + ...

No CASE needed here.

COALESCE is similar to ISNULL and would usually be recommended except for a few odd situations – for one, it’s part of standard SQL (useful if you ever have to work against other RDBMSes), for another it can accept multiple arguments and returns the first non-NULL one. For a third, it uses the most appropriate data type for the result considering the types of each expression – ISNULL always tries to convert the second argument to the type of the first)

---

(I’m also not sure what you we’re doing in your CASE expressions – you’d already established that, e.g. OCAREOF was null – there was no need to then use an ISNULL expression to obtain '')

---

(*) As Conrad points out, on SQL Server this does depend on CONCAT_NULL_YIELDS_NULL being ON, but it is by default and it really should be:

In a future version of SQL Server CONCAT_NULL_YIELDS_NULL will always be ON and any applications that explicitly set the option to OFF will generate an error. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.