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outer join
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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