LEFT JOIN

Question

LEFT JOIN

branovuk

SSCommitted

Points: 1774
More actions
June 9, 2010 at 8:07 am

#236274

Hello, it looks like simple issue, but not for me :(:
Table1:
SELECT *
FROM Table1
______________
87000 rows
SELECT *
FROM Table1
LEFT JOIN Table2 on Table1.ID = Table2.ID
______________
99000 rows
It should be the same numbers?
What am I missing?

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J-F Bergeron SSCrazy Eights Points: 8593 More actions · Answer 1

You have duplicate ID in the table 2, therefore, the left join is showing you every match from table1, that has been found, or not, in table 2. If there are duplicates on your join, they will be present.

Cheers,

J-F

branovuk SSCommitted Points: 1774 More actions · Answer 2

Thanks J-F,

That is my misunderstanding of LEFT JOIN.

And I found better explanation of LEFT JOIN. I didn't count that "situation", when I can have duplicate in Table2.

In my case, it should be highly unlikely, since it is product name in Table2. It looks like couple of thousand products with more than one name.

Regards,

Brano