Mensaje
De
15/03/2010 11:38:41
 
General information
Foro:
Visual FoxPro
Category:
Bases de datos, tablas, vistas, índices y SQL
Miscellaneous
ID de la conversación:
01454516
ID del mensaje:
01454564
Views:
45
>>>There're at least 3 ways you can do that
>>>
>>>* 1 - EXISTS subquery
>>>SELECT * FROM mytable1 WHERE NOT EXISTS (SELECT 1 FROM mytable2 WHERE myfield1 = mytable1.myfield1)
>>>* 2 - JOIN
>>>SELECT mytable1.* FROM mytable1 JOIN mytable2 ON mytable2.myfield1 = mytable1.myfield1 ;
>>>  WHERE mytable2.myfield1 IS NULL
>>>* 3 - IN subquery
>>>SELECT * FROM mytable1 WHERE myfield1 NOT IN (SELECT myfield1 FROM mytable2)
>>>
>>>The second one most likely will be the fastest in VFP
>>>
>>
>>
>>Shouldn't #2 be a left join ?
>
>Yes, it should be a LEFT JOIN (was a typo, I assume). Check this link http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/the-ten-most-asked-sql-server-questions--1#4


bu-bu-but i like number 3 and number 1 must i use number 2?
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