Can SQL Join Tables Across Different Databases?

Joining Tables from Different Databases

Can SQL join operations be performed across tables from different databases? If so, how is it achieved?

Answer:

Yes, SQL Server enables the joining of tables from separate databases residing on the same server. The modified join procedure is as follows:

Full Table Name Qualification:

In inter-database joins, it's essential to fully qualify table names by specifying both the database name and the table schema (if applicable). This ensures SQL Server can unequivocally identify the tables being joined.

Example:

Consider two databases on the same server: Db1 and Db2. Db1 contains a "Clients" table with a "ClientId" column, while Db2 has a "Messages" table with a "ClientId" column.

Join Query:

select *
from Db1.dbo.Clients c
join Db2.dbo.Messages m on c.ClientId = m.ClientId

In this query, the "dbo" schema is explicitly specified for both tables, as it's the default schema in SQL Server. By qualifying the table names with their respective database names, the join operation can successfully link tables from different databases.

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