Tidak dapat menggunakan kolom sementara di klausa mana?

Salah satu solusinya adalah membuat subselect dari seluruh pernyataan, menerapkan klausa where pada hasilnya

select  *
from    (
          select  cast(de.ApprovalOrder AS VARCHAR(32)) 
                  + cast(de.EntityCode AS VARCHAR(32)) 
                  + isnull(cast(de.DelegationCode AS VARCHAR(32)), '') as 'RowID'
                  , *
          from    workflow.delegation_engine de
        ) de 
where   de.RowID IS NOT NULL

Solusi lain adalah mengulang seluruh klausa dalam klausa WHERE

select  cast(de.ApprovalOrder AS VARCHAR(32)) 
        + cast(de.EntityCode AS VARCHAR(32)) 
        + isnull(cast(de.DelegationCode AS VARCHAR(32)), '') as 'RowID' ,
        *
from    workflow.delegation_engine de
where   cast(de.ApprovalOrder AS VARCHAR(32)) 
        + cast(de.EntityCode AS VARCHAR(32)) 
        + isnull(cast(de.DelegationCode AS VARCHAR(32)), '') IS NOT NULL

Atau Anda dapat menguji setiap bidang individu untuk NULL

select  cast(de.ApprovalOrder AS VARCHAR(32)) 
        + cast(de.EntityCode AS VARCHAR(32)) 
        + isnull(cast(de.DelegationCode AS VARCHAR(32)), '') as 'RowID' ,
        *
from    workflow.delegation_engine de
where   de.ApprovalOrder IS NOT NULL
        AND de.EntityCode IS NOT NULL