Check Constraint : col1 Null if col2 Not Null

RomainH

Hi everyone,

I can't found how I can do this,

It seems to me, a python script can not do that because it can not return a null value...

Is there a workaround or something that makes it possible?

Thanks

Alex B

Hi @RomainH,

You can return DBNull like this to return NULL

return DBNull

But I couldn't get a check for a row value of NULL to work.  I tried

val is None
val is not None
val is DBNull
val is DBNull.Value
val == DBNull
val == DBNull.Value

But couldn't get it to work.

If I did 

def main(config):
        if (col2 == "notnull   "):
        return 4
    else:
        return DBNull
    return 0<br>

Then it would correctly place null or the number 4
​

But that required me to know the value of col2 to check against.

So I'm not sure what might work here, perhaps you have solved that part of it and just returning DBNull will get you there, if so please let us know!

Kind regards,
Alex

pdb

Alex B said:

But I couldn't get a check for a row value of NULL to work.  I tried

val is None
val is not None
val is DBNull
val is DBNull.Value
val == DBNull
val == DBNull.Value

But couldn't get it to work.

Hello, I am struggeling with the same issue. Are there any updates on "how to check another column value for null within a python script"?

EDIT: Finally found out myself. We need to use

val.IsNull

Found it by accident. Where is a documentation for that?