Join two sys.columns tables from different servers - sql

Question

I have two similar dbs on two different servers. I'm trying to join their sys.columns tables, but I don't understand why this wouldn't work
SELECT *
FROM server1.db1.sys.columns t
INNER JOIN server2.db2.sys.columns s
ON OBJECT_NAME(t.[object_id]) = OBJECT_NAME(s.[object_id])
AND t.name = s.name
WHERE OBJECT_NAME(t.[object_id]) = 'commonTable'
commonTable exists in both dbs. Above query returns empty set
I join on OBJECT_NAME because their object_ids obviously different, since they are located on different dbs, so I join on their names in that way

Answer 1

OBJECT_NAME() works locally so it is never going to return the name of some object id in another database. Join to the foreign sys.columns and sys.objects view.
SELECT *
FROM server1.db1.sys.columns AS loc_c
INNER JOIN server2.db2.sys.columns AS rem_c
ON loc_c.name = rem_c.name
INNER JOIN server1.db1.sys.tables AS loc_t
ON loc_t.[object_id] = loc_c.[object_id]
INNER JOIN server2.db2.sys.tables AS rem_t
ON loc_t.name = rem_t.name
AND rem_t.[object_id] = rem_c.[object_id]
WHERE loc_t.name = N'commonTable';
You may want to add local and remote joins to sys.schemas, too, since dbo.foo and otherschema.foo will both match.
You may also consider synonyms and/or views to reduce complexity, if you are doing this a lot.
CREATE VIEW dbo.server1cols
AS
SELECT [table] = loc_t.name, [column] = loc_c.name
FROM server1.db1.sys.columns AS loc_c
INNER JOIN server1.db1.sys.tables AS loc_t
ON loc_t.[object_id] = loc_c.[object_id];
GO
CREATE VIEW dbo.server2cols
AS
SELECT [table] = rem_t.name, [column] = rem_c.name
FROM server2.db2.sys.columns AS rem_c
INNER JOIN server2.db2.sys.tables AS rem_t
ON rem_t.[object_id] = rem_c.[object_id];
GO
CREATE VIEW dbo.MatchDB1DB2Cols
AS
SELECT s1.[table],
db1column = s1.[column],
db2column = s2.[column]
FROM dbo.server1cols AS s1
INNER JOIN dbo.server2cols AS s2
ON s1.[table] = s2.[table]
AND s1.[column] = s2.[column];
GO
Now your query is simply:
SELECT [table], db1column, db2column
FROM dbo.MatchDB1DB2Cols
WHERE [table] = N'commonTable';
You may also want to consider a full outer join somewhere so you can also note differences between the tables.