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I’m trying to get all distinct values across 2 tables using a union.
The idea is to get a count of all unique values in the columnA column without repeats so that I can get a summation of all columns that contain a unique columnA.
This is what I tried (sql server express 2008)
select
count(Distinct ColumnA)
from
(
select Distinct ColumnA as ColumnA from tableX where x = y
union
select Distinct ColumnA as ColumnA from tableY where y=z
)
The extra distincts on TableX and TableY aren’t necessary; they’ll get stripped in the tmp.ColumnA clause. Declaring a temporary table should eliminate the ambiguity that might’ve prevented your query from executing.