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Posted by Hugo Kornelis on 09/30/05 22:39
On 30 Sep 2005 01:36:49 -0400, Joseph wrote:
>Hi,
>I dont know to write SQL command filter.
>m_strQueryDelete.Format("DELETE FROM tab WHERE (Col1 = abc AND Col2
>= abc AND ?????)"
>example: ODBC found 100 records.
>I need to delete first 90 records and to leave last 10 records.
>
>Thank you
>
>Joseph
Hi Joseph,
Define: "first 90". You see, tables in the relational model are, by
definition, UNordered collections of data. There is no such thing as
"first" or "last" until you define an ordering.
For example, if you have a column EntryDate in your table and you want
to delete the 90 oldest rows that have 'abc' in both Col1 and Col2, you
would use:
DELETE FROM tab
WHERE Col1 = 'abc'
AND Col2 = 'abc'
AND (SELECT COUNT(*)
FROM tab AS t2
WHERE t2.Col1 = 'abc'
AND t2.Col2 = 'abc'
AND t2.EntryDate <= tab.EntryDate) <= 90
Best, Hugo
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