Question

A puzzler from a coworker that I cannot figure out…

update  btd.dbo.tblpayroll set     empname = ( select  b.Legal_Name                     from    ( SELECT    Legal_Name,                                         Employee_ID                               FROM      Com.dbo.Workers                               WHERE     isnumeric(Employee_ID) = 1                             ) b                     where   b.Employee_ID = empnum                             and b.Legal_name is not NULL                   ) where   empname is NULL 

---

Msg 245, Level 16, State 1, Line 1 Conversion failed when converting the varchar value ‘N0007 ‘ to data type int. The table alias b would actually be a view.

The value ‘N0007 ‘ is in the Workers table. I don’t see why it is not being filtered from the results that are being joined.

EDIT:

The alias does, in fact, return the correct rows – so isNumeric is doing the job.

Answer 1

I suspect that the optimizer is attempting to apply the where clause of the outer select before the inner select. Presumably it thinks it would be able to do an index lookup on Employee_ID resulting in a faster query in this case. Try:

update  btd.dbo.tblpayroll set     empname = ( select Legal_Name                     from Com.dbo.Workers                     where  isnumeric(Employee_ID) = 1                            and convert(varchar,Employee_ID)                              = convert(varchar,empnum)                             and Legal_name is not NULL) where   empname is NULL 

Converting them all to varchar should take care of it. I don’t think it’s much less efficient than you wanted orginally since the isnumeric, if done first, would have forced a table scan anyway.