outer join
In relational databases, a join that returns all rows from one table and matched rows from another, with NULLs where no match exists. Often specified as LEFT, RIGHT, or FULL outer join.
Using an outer join in SQL, you can retrieve data even when there is no matching row in one of the tables.
external coupling; external linkage
General engineering term for a connection or linkage between separate systems or components. Less common than the database sense; context usually makes the meaning clear.
This machine works together with another device through an external coupling.