>>UNION will filter the duplicate records, BUT you will never have ones, because of CAST('' AS char(50))
>>
>>

>>SELECT 1, 'abracadabra'
>>UNION
>>SELECT 1, ''
>>

>>will generate two records
>
>I see now, you're right. We do need a left join in the second portion with is null in where clause.

Ergo your original assertion is false, which is exactly what I figured.