Thread View: comp.lang.pascal.delphi.databases
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Started by Dominik L�bbers
Wed, 03 Feb 1999 00:00
Outer Joins in BDE - maybe a bug
Author: Dominik L�bbers
Date: Wed, 03 Feb 1999 00:00
Date: Wed, 03 Feb 1999 00:00
44 lines
1988 bytes
1988 bytes
Using SQL-Language of the BDE the following problems occured: Guess, we have 3 tables: 1) "Teachers" with a fields ID and a name 2) "Courses" with a field ID, a name and a Teacher-ID 3) "Students" with a field ID, a name and a Course-ID For example these tables content the following data: Teachers ======== ID Name 99 Smith Courses ======= ID Name Teacher 1 Course 1 Students ======== ID Name Course 900 Bart Simpson 1 Notice, that no Teacher-ID is given in the Courses-Table. In this situation the following SQL-Queries give a different result: SELECT * FROM (Courses C INNER JOIN Students S ON S.Course=C.ID) LEFT OUTER JOIN Teachers T ON C.Teacher=T.ID SELECT * FROM (Courses C LEFT OUTER JOIN Teachers T ON C.Teacher=T.ID) INNER JOIN Students S ON S.Course=C.ID In the second case a sentence is given back, in the first case not. Should'nt this be the same? And if not, why not? Hoping, someone find the difference and tells me what to do. Thanks Dominik Luebbers
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