INNER JOIN operation
VALUES (1,2,3)
SELECT DISTINCT A.ORIG_AIRPORT, B.FLIGHT_ID FROM
(SELECT FLIGHT_ID, ORIG_AIRPORT
FROM FLIGHTS
ORDER BY ORIG_AIRPORT DESC
FETCH FIRST 40 ROWS ONLY)
AS A, FLIGHTAVAILABILITY AS B
WHERE A.FLIGHT_ID = B.FLIGHT_ID
-- List the employee numbers (EMPNO) of all employees in the EMPLOYEE
-- table whose department number (WORKDEPT) either begins with 'E' or
-- who are assigned to projects in the EMP_ACT table
-- whose project number (PROJNO) equals 'MA2100', 'MA2110', or 'MA2112'
SELECT EMPNO
FROM EMPLOYEE
WHERE WORKDEPT LIKE 'E%'
UNION
SELECT EMPNO
FROM EMP_ACT
WHERE PROJNO IN('MA2100', 'MA2110', 'MA2112')
-- Make the same query as in the previous example
-- and "tag" the rows from the EMPLOYEE table with 'emp' and
-- the rows from the EMP_ACT table with 'emp_act'.
-- Unlike the result from the previous example,
-- this query may return the same EMPNO more than once,
-- identifying which table it came from by the associated "tag"
SELECT EMPNO, 'emp'
FROM EMPLOYEE
WHERE WORKDEPT LIKE 'E%'
UNION
SELECT EMPNO, 'emp_act' FROM EMP_ACT
WHERE PROJNO IN('MA2100', 'MA2110', 'MA2112')
-- Make the same query as in the previous example,
-- only use UNION ALL so that no duplicate rows are eliminated
SELECT EMPNO
FROM EMPLOYEE
WHERE WORKDEPT LIKE 'E%'
UNION ALL
SELECT EMPNO
FROM EMP_ACT
WHERE PROJNO IN('MA2100', 'MA2110', 'MA2112')
-- Make the same query as in the previous example,
-- only include an additional two employees currently not in any table
-- and tag these rows as "new"
SELECT EMPNO, 'emp'
FROM EMPLOYEE
WHERE WORKDEPT LIKE 'E%'
UNION
SELECT EMPNO, 'emp_act'
FROM EMP_ACT
WHERE PROJNO IN('MA2100', 'MA2110', 'MA2112')
UNION
VALUES ('NEWAAA', 'new'), ('NEWBBB', 'new')
ScalarSubquery turns a