Inayotaka kusoma kwa LEFT JOIN kwa SQL

Inayotaka kusoma kwa LEFT JOIN kwa SQL

LEFT JOIN kibidi chuki kinachotumia kila mengine wa kati ya tabia ya kwanza (table_name1), bila kumekuwa mifano kati ya tabia ya kwanza (table_name2).

Makosa ya neno la kigeukia la LEFT JOIN

SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name

Mawazo:Kwenye database zao, LEFT JOIN inaitwa LEFT OUTER JOIN.

Jadual lake la kwanza (lilitumika kwenye mifano):

Jadual la "Persons":

Id_P LastName FirstName Address City
1 Adams John Oxford Street London
2 Bush George Fifth Avenue New York
3 Carter Thomas Changan Street Beijing

Jadual la "Orders":

Id_O OrderNo Id_P
1 77895 3
2 44678 3
3 22456 1
4 24562 1
5 34764 65

Mifano wa kigeukia kwa kikomo (LEFT JOIN)

Sasa, tunataka kuonyesha watu wote, na maodishi yao - kama yana maodishi.

Unaweza kutumia mambo ya SELECT hii:

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
LEFT JOIN Orders
ON Persons.Id_P=Orders.Id_P
ORDER BY Persons.LastName

Matokeo ya mifano:

LastName FirstName OrderNo
Adams John 22456
Adams John 24562
Carter Thomas 77895
Carter Thomas 44678
Bush George 　

Neno la kigeukia la LEFT JOIN kinasababisha kurejea kila barua kutoka kwenye jadual la kwanza (Persons), bila kufikiria barua zilizojifanyia kwenye jadual la pili (Orders).