Question

Original Question:

I am new to SQL server and can’t quite find what I am looking for. I’m trying to create this logic in SQL:

IF [column] IS NULL THEN
    ( SELECT [value] as [columnname] )
ELSE
    ( SELECT [column] WHERE [column_value] IS NOT NULL )

Basically, if an entire column is null, I want to select and fill the whole column with a certain value.

Else, if that column is not completely null, I only want to select its non-null values (coalesce?).

What is the best way to do this using SQL Server 2005?

Answer (thanks to Josh and everyone else!)

IF EXISTS(SELECT myColumn
          FROM mytable
          WHERE myColumn IS NOT NULL)
    SELECT myColumn as colName
    FROM myTable
    WHERE myColumn is NOT NULL
ELSE
    SELECT [nullReplacementValue] as colName
    FROM myTable

Earlier clarification for the confused:

EDIT: For example, if I were given an input table as such:

ColA    ColB    ColC
--------------------
A       null    null
B       null    1
C       null    null

If I were running this SELECT on ColB, it should return:

ColB
----
null
null
null

(eventually I’d like to replace “null” with some value but that can come later).

If I were running this SELECT on ColC, it should return:

ColC
----
1

Answer 1

If you’re simply asking about a way to default values in a known column if all values in the column are NULL then you can use this:

IF EXISTS(SELECT myColumn FROM mytable WHERE myColumn IS NOT NULL)
    SELECT myColumn FROM myTable WHERE myColumn is NOT NULL
ELSE
    UPDATE myTable SET myColumn = myValue

This is checking to see if at least one value in the column you care about is not null. If it is that means you want to select. Else, you’ll update all the columns because you didn’t return a result when asking for columns that are not null.