The CData ADO.NET Provider for LDAP supports standard SQL joins like the following examples.

Inner Join

An inner join selects only rows from both tables that match the join condition:

SELECT Group.AdminDisplayName, User.AdminDisplayName FROM Group, User WHERE Group.Id = User.PrimaryGroupId

Left Join

A left join selects all rows in the FROM table and only matching rows in the JOIN table:

SELECT Group.AdminDisplayName, User.AdminDisplayName FROM Group LEFT OUTER JOIN User ON Group.Id=User.PrimaryGroupId