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cwtriguns2002
Constraint Violating Yak Guru
272 Posts |
 Posted - 2007-02-21 : 01:11:21
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| Hello everyone. What is meant by left join, right join, and cross join, etc...? Sorry for the question. Im using SQL 2005 for just 6 months, and only the INNER JOIN i know.Thanks,Ron |
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harsh_athalye
Master Smack Fu Yak Hacker
5581 Posts |
Posted - 2007-02-21 : 01:13:58
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| [url]http://www.microsoft.com/technet/technetmag/issues/2005/05/HowITWorksSQLJoins/?related=/technet/technetmag/issues/2005/05/HowITWorksSQLJoins[/url]Harsh AthalyeIndia."The IMPOSSIBLE is often UNTRIED" |
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cwtriguns2002
Constraint Violating Yak Guru
272 Posts |
Posted - 2007-02-21 : 01:51:53
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Ok Thanks Harsh. I have read the page, but I can't totally absorb how the cross join really works. And other thing is, why is it a need to use cross join?quote:
Cross Join - A cross join returns not the sum but the product of two tables. Each row in the left-hand table is matched up with each row in the right-hand table. It's the set of all possible row combinations, without any filtering, as shown here: SELECT au_fname, au_lname, pub_nameFROM authors CROSS JOIN publishers ORDER BY au_lname DESCThe resultset contains 184 rows (authors has 23 rows, and publishers has 8; therefore, 23 × 8 = 184). The first 11 rows look like au_fname au_lname pub_name Akiko Yokomoto New Moon Books Akiko Yokomoto Binnet & Hardley Akiko Yokomoto Algodata Infosystems Akiko Yokomoto Five Lakes Publishing Akiko Yokomoto Ramona Publishers Akiko Yokomoto GGG&G Akiko Yokomoto Scootney Books Akiko Yokomoto Lucerne Publishing Johnson White New Moon Books Johnson White Binnet & Hardley Johnson White Algodata Infosystems
In the example above, i can't get the idea you need to use cross join, in fact you are just assigning the author to all publisher... Thanks,Ron |
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harsh_athalye
Master Smack Fu Yak Hacker
5581 Posts |
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