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Ñòàòèñòèêà LiveInternet.ru: ïîêàçàíî êîëè÷åñòâî õèòîâ è ïîñåòèòåëåé
Ñîçäàí: 16.03.2006
Çàïèñåé:
Êîììåíòàðèåâ:
Íàïèñàíî: 4


Ñòðàííûé âûâîä çàïðîñà.

Âòîðíèê, 30 Ìàÿ 2017 ã. 15:32 + â öèòàòíèê
 áàçå äàííûõ ïîñòðîåíû äâà çàïðîñà, êàæäûé èç êîòîðûõ ñîáèðàåò íåêîòîðûé íàáîð çàïèñåé.
Ýòè çàïðîñû èñïîëüçóþòñÿ êàê èñòî÷íèê äàííûõ òðåòüåãî çàïðîñà, ïðè÷¸ì ïðèìåíÿåòñÿ LEFT JOIN. Ñîîòâåòñòâåííî ÿ îæèäàþ, ÷òî äëÿ òåõ çàïèñåé îäíîãî ïîäçàïðîñà, êîòîðûì íåò ñîîòâåòñòâèÿ âî âòîðîì ïîäçàïðîñå, íà ìåñòå ïîëåé âûâîäà èç âòîðîãî ïîäçàïðîñà áóäåò Null... à âîò õðåí! È ÿ íå ïîíèìàþ, ïî÷åìó...

Òåïåðü êîíêðåòíî.

Âîò ïåðâûé ïîäçàïðîñ
+ SubQuery1
SELECT Ïàíåëè.Íàèìåíîâàíèå & ' - ' & Ïîðòû.Ïîðò AS Ïîðò1, Ïîðòû.Êîä
FROM Ïàíåëè 
INNER JOIN Ïîðòû ON Ïàíåëè.Êîä = Ïîðòû.Ïàíåëü

Âîò âòîðîé ïîäçàïðîñ
+ SubQuery2
SELECT Êðîññèðîâêè.Ïîðò1, Ïàíåëè.Íàèìåíîâàíèå & ' - ' & Ïîðòû.Ïîðò AS Ïîðò2
FROM Ïàíåëè 
INNER JOIN 	(
			Ïîðòû 
			INNER JOIN Êðîññèðîâêè ON Ïîðòû.Êîä = Êðîññèðîâêè.Ïîðò2
			) ON Ïàíåëè.Êîä = Ïîðòû.Ïàíåëü

Âîò çàïðîñ, èñïîëüçóþùèé èõ:
+ Êðîññèðîâàíèå-1
SELECT SubQuery1.Ïîðò1 AS Ïîðò1, SubQuery2.Ïîðò2 AS Ïîðò2, SubQuery1.Êîä AS Êîä1, SubQuery2.Ïîðò1 AS Êîä2
FROM SubQuery1 
LEFT JOIN SubQuery2 ON SubQuery1.Êîä = SubQuery2.Ïîðò1;

èëè îí æå, íî ñ ïîäñòàíîâêîé òåêñòà:
+ Êðîññèðîâàíèå-2
SELECT SubQuery1.Ïîðò1 AS Ïîðò1, SubQuery2.Ïîðò2 AS Ïîðò2, SubQuery1.Êîä AS Êîä1, SubQuery2.Ïîðò1 AS Êîä2
FROM 	(
		SELECT Ïàíåëè.Íàèìåíîâàíèå & ' - ' & Ïîðòû.Ïîðò AS Ïîðò1, Ïîðòû.Êîä
		FROM Ïàíåëè 
		INNER JOIN Ïîðòû ON Ïàíåëè.Êîä = Ïîðòû.Ïàíåëü
		) AS SubQuery1 
LEFT JOIN 	(
			SELECT Êðîññèðîâêè.Ïîðò1, Ïàíåëè.Íàèìåíîâàíèå & ' - ' & Ïîðòû.Ïîðò AS Ïîðò2
			FROM Ïàíåëè 
			INNER JOIN 	(
						Ïîðòû 
						INNER JOIN Êðîññèðîâêè ON Ïîðòû.Êîä = Êðîññèðîâêè.Ïîðò2
						) ON Ïàíåëè.Êîä = Ïîðòû.Ïàíåëü
			) AS SubQuery2 ON SubQuery1.Êîä = SubQuery2.Ïîðò1;


Ïîíÿòíî, äëÿ òåõ çàïèñåé ïåðâîãî ïîäçàïðîñà, êîòîðûì íåò ñîîòâåòñòâèÿ âî âòîðîì, ÿ â ïîëÿõ SubQuery2.Ïîðò2 AS Ïîðò2 è SubQuery2.Ïîðò1 AS Êîä2 îæèäàþ óâèäåòü Null... è â ïîëå SubQuery2.Ïîðò1 AS Êîä2 ÿ ýòîò Null è ïîëó÷àþ... íî âèæó âìåñòî íåãî â ïîëå SubQuery2.Ïîðò2 AS Ïîðò2 ëèòåðàë " - ".

Íàáëþäåíèå äåìîíñòðèðóåò ñêðèíøîò ("Êðîññèðîâàíèå-2" - ýòî èìÿ ñîõðàí¸ííîãî ñòàòè÷åñêè ïîñëåäíåãî çàïðîñà, êîòîðûé ñ ïîäñòàíîâêàìè).

ÏÎ×ÅÌÓ???

http://www.sql.ru/forum/1261598/strannyy-vyvod-zaprosa


 

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