LEFT OUTER JOIN in Teradata

The result of a left outer join (or simply left join) for table A and B always contains all records of the "left" table (A), even if the join-condition does not find any matching record in the "right" table (B). This means that if the ON clause matches 0 (zero) records in B (for a given record in A), the join will still return a row in the result (for that record)—but with NULL in each column from B.
A left outer join returns all the values from an inner join plus all values in the left table that do not match to the right table.

Consider the following two tables,
Employee table
LastNameDepartmentID
Rafferty31
Jones33
Steinberg33
Robert34
Smith34
JohnNULL


Department table
DepartmentIDDepartmentName
31Sales
33Engineering
34Clerical
35Marketing


SELECT *
FROM employee
LEFT OUTER JOIN department ON employee.DepartmentID = department.DepartmentID;


Output:
Employee.LastNameEmployee.DepartmentIDDepartment.DepartmentNameDepartment.DepartmentID
Jones33Engineering33
Rafferty31Sales31
Robert34Clerical34
Smith34Clerical34
JohnNULLNULLNULL
Steinberg33Engineering33