UNION ALL in Teradata

UNION ALL will not filter the duplicate rows where UNION filters.
When user wants to find all the values(including duplicates) from two or more tables then UNION ALL can be supplied.

Sample syntax:
SELECT column(s)
FROM
tbl_name1 WHERE condition
UNION ALL
SELECT column(s)
FROM
tbl_name2 WHERE condition


Example:
List the names of all employees present in company1 and company2.
Here, the names of employees may be same between the two companies.
However user wants all the names of employees with company id.
(Note that company_id is given here for identifying the repeated employee names)

SELECT employee_name, company_id
FROM
tbl_company1
UNION ALL
SELECT employee_name, company_id
FROM
tbl_company2


Note: ORDER BY cannot be supplied over UNION ALL statement.