Ñàìîñîåäèíåíèÿ
 íåêîòîðûõ çàäà÷àõ íåîáõîäèìî ïîëó÷èòü èíôîðìàöèþ, âûáðàííóþ îñîáûì îáðàçîì òîëüêî èç îäíîé òàáëèöû. Äëÿ ýòîãî èñïîëüçóþòñÿ òàê íàçûâàåìûå ñàìîñîåäèíåíèÿ, èëè ðåôëåêñèâíûå ñîåäèíåíèÿ. Ýòî íå îòäåëüíûé âèä ñîåäèíåíèÿ, à ïðîñòî ñîåäèíåíèå òàáëèöû ñ ñîáîé ñ ïîìîùüþ àëèàñîâ. Ñàìîñîåäèíåíèÿ ïîëåçíû â ñëó÷àÿõ, êîãäà íóæíî ïîëó÷èòü ïàðû àíàëîãè÷íûõ ýëåìåíòîâ èç îäíîé è òîé æå òàáëèöû.
SELECT one.last_name, two.last_name,
one.hire_date
FROM employee one, employee two
WHERE one.hire_date = two.hire_date
AND one.emp_no < two.emp_no
ïîëó÷èòü ïàðû ôàìèëèé ñîòðóäíèêîâ,
êîòîðûå ïðèíÿòû íà ðàáîòó â îäèí
è òîò æå äåíü
LAST_NAME LAST_NAME HIRE_DATE
==================== ==================== ===========
Nelson Young 28-DEC-1988
Reeves Stansbury 25-APR-1991
Bishop MacDonald 1-JUN-1992
Brown Ichida 4-FEB-1993
SELECT d1.department, d2.department, d1.budget
FROM department d1, department d2
WHERE d1.budget = d2.budget
AND d1.dept_no < d2.dept_no
ïîëó÷èòü ñïèñîê ïàð îòäåëîâ ñ
îäèíàêîâûìè ãîäîâûìè áþäæåòàìè
DEPARTMENT DEPARTMENT BUDGET
======================== ========================= =========
Software Development Finance 400000.00
Field Office: East Coast Field Office: Canada 500000.00
Field Office: Japan Field Office: East Coast 500000.00
Field Office: Japan Field Office: Canada 500000.00
Field Office: Japan Field Office: Switzerland 500000.00
Field Office: Singapore Quality Assurance 300000.00
Field Office: Switzerland Field Office: East Coast 500000.00
