Question

I have 4 databases with similar schema’s, and I’m trying to create a query to return just the table, column pairs that exist ONLY in database 1 and do not exist in database 2, 3, or 4.

Currently I can return the symmetric difference between database 1 and 2 via the following query…

select table_name, column_name from (         select table_name, column_name from [Database1].information_schema.columns         union all         select table_name, column_name from [Database2].information_schema.columns) as tmp         group by table_name, column_name having count(*) = 1 

However, in trying to isolate just those columns in database 1, and doing the same across all 4 databases, things are getting complicated. What is the cleanest solution for this query?

Answer 1

SELECT      D1.table_name,      D1.column_name FROM      Database1.information_schema.columns D1 LEFT OUTER JOIN Database2.information_schema.columns D2 ON      D2.table_name = D1.table_name AND      D2.column_name = D1.column_name LEFT OUTER JOIN Database3.information_schema.columns D3 ON      D3.table_name = D1.table_name AND      D3.column_name = D1.column_name LEFT OUTER JOIN Database4.information_schema.columns D4 ON      D4.table_name = D1.table_name AND      D4.column_name = D1.column_name WHERE      D2.table_name IS NULL AND      D3.table_name IS NULL AND      D4.table_name IS NULL