StackOverflow2013

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plurals

PO
primarykey
Id
16530136
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
2
CommunityOwnedDate
CreationDate
2013-05-13T19:59:21.280
FavoriteCount
0
LastActivityDate
2013-05-13T21:21:31.740
LastEditDate
2013-05-13T21:21:31.740
LastEditorUserId
2246674
OwnerUserId
2246674
ParentId
16530003
PostTypeId
2
Score
3
ViewCount
0
LastEditorDisplayName
text
Body
The only way that the queries would have the same results is if the <code>tareas</code> join matched every record (in the preceding from..inner join set) exactly once. If the first query results in more rows, then the <code>tareas</code> contains duplicates records per the join predicate (i.e. it has duplicate <code>idclientecrm</code> values). This why the records must be matched exactly once for the same result set. (If this was meant to be a 1-1 relationship then some constraints were not setup correctly .. whoops!) Consider this simple <a href="http://en.wikipedia.org/wiki/Join_%28SQL%29#Inner_join" rel="nofollow">inner join</a> example showing the outcome with different multiplicities: <pre><code>A <- { 1, 2, 4 } B <- { 1, 2(#1), 2(#2), 3 } A join B => { 1, 2(#1), 2(#2) } </code></pre> Reason for result: <ul> <li>A.1 match B.1 - this is the only record that matched exactly once</li> <li>A.2 match B.2(#1)</li> <li>A.2 match B.2(#2)</li> <li>A.4 no match</li> <li>B.3 no match</li> </ul> I think that this excerpt from Wikipedia explains the concept well: <blockquote> The result of the join can be defined as the outcome of first taking the Cartesian product (or Cross join) of all records in the tables (combining every record in table A with every record in table B)—then return all records which satisfy the join predicate. </blockquote> (This why a CROSS JOIN with a WHERE can return the same results as an INNER JOIN - ick, though!)
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singulars
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1. This table or related slice is empty.
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1. PODifference between two queries
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1. PTAnswer
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1. USuser2246674
UserOwnerUserId
1. USuser2246674
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1. PODifference between two queries
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2. VO
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3. VO
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CommentsPostId
1. COexcellent example. Helped me understand very clearly the difference. Thnx
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 USPietro
2. CO@Pietro You're welcome :D
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