Cross-platform SQL date difference function or query

I have a table that has a datetime column and I need to retrieve records with a date within the previous hour, day, week, month etc.

One constraint is that I need to support Oracle, MySQL, DB2 and SQL SERVE开发者_如何学CR. Can I achieve this with one SQL query only?

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Since they all can handle datetimes differently, I'm going to guess you can't. You might be able to separate out the platform-specific stuff and swap it when the platform changes.

If you tell us more about this problem, we might be able to suggest something in more detail.

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User-defined functions. Write your own DATEDIFF-equivalent for each RDBMS and abstract away the differences.

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This sounds like a good reason to start up on a multi-tiered RDBMS-based-approach to retrieving data.

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The ANSI SQL function would be datediff(). But I doubt all (especially older) SQL dialects support it.