outer join

database A less commonly used variant of the inner join

relational database operation. An inner join selects rows

from two tables such that the value in one column of the

first table also appears in a certain column of the second

table. For an outer join, the result also includes all rows

from the first operand ("left outer join", "*="), or the

second operand ("right outer join", "=*"), or both ("full

outer join", "*=*"). A field in a result row will be null if

the corresponding input table did not contain a matching row.

For example, if we want to list all employees and their

employee number, but not all employees have a number, then we

could say (in SQL):

SELECT employee.name, empnum.number

WHERE employee.id *= empnum.id

The "*=" means "left outer join" and means that all rows from

the "employee" table will appear in the result, even if there

is no match for their ID in the empnum table.

(2001-03-23)