Assume you have two database, Db1 and Db2.
Employee table is in Db1 and Department in Db2
Query:
select emp_name, dept_name from Db1.dbo.Employee a, Db2.dbo.Department b where a.dept_id = b.dept_id
Syntax is Database name followed by .dbo. followed by table name
eg. Db1.dbo.Employee
Similarly you can use above syntax for any type of query.
Employee table is in Db1 and Department in Db2
Query:
select emp_name, dept_name from Db1.dbo.Employee a, Db2.dbo.Department b where a.dept_id = b.dept_id
Syntax is Database name followed by .dbo. followed by table name
eg. Db1.dbo.Employee
Similarly you can use above syntax for any type of query.