Left Join Question
От | Ryan Wells |
---|---|
Тема | Left Join Question |
Дата | |
Msg-id | 52F2AD70C422474B857FC9E3F7B62539028DB1E8@exchange.DOCS.COM обсуждение исходный текст |
Ответы |
Re: Left Join Question
Re: Left Join Question Re: Left Join Question |
Список | pgsql-sql |
<div class="Section1"><p class="MsoNormal">While looking through our data layer code today, I ran across this query:<p class="MsoNormal"> <pclass="MsoNormal">SELECT <p class="MsoNormal">tasks.*,<p class="MsoNormal">clients.FirstName,<p class="MsoNormal">clients.LastName,<pclass="MsoNormal">clients.MiddleInitial,<p class="MsoNormal">iteminfo.CreatedBy,<p class="MsoNormal">iteminfo.StationId,<pclass="MsoNormal">iteminfo.CreatedDate,<p class="MsoNormal">changelog.LastModified,<pclass="MsoNormal">changelog.LastModifiedBy,<p class="MsoNormal">changelog.LastModifiedAt,<pclass="MsoNormal">ticklers.Due,<p class="MsoNormal">ticklers.Reminder<p class="MsoNormal"> <pclass="MsoNormal">FROM tasks <p class="MsoNormal"> LEFT JOIN clients ON tasks.ClientId = clients.ClientId<p class="MsoNormal"> LEFT JOIN iteminfo ON tasks.Id = iteminfo.ItemId <p class="MsoNormal"> LEFT JOINchangelog ON tasks.Id = changelog.ItemId <p class="MsoNormal"> LEFT JOIN ticklers ON tasks.Id = ticklers.RelatedId<p class="MsoNormal"> <p class="MsoNormal">WHERE tasks.Id = '123456';<p class="MsoNormal"> <p class="MsoNormal">(I'vecleaned it up so it's easier to read.)<p class="MsoNormal"> <p class="MsoNormal">The basic data structureis that we have a todo list that contains a list of tasks which may or may not be associated with clients, items,log entries, or ticklers (scheduled reminders). <p class="MsoNormal"> <p class="MsoNormal">The query works as intended: it returns a result-set with all the necessary data to display in the todo list. The performance is not a majorconcern, although it can be slow for large lists.<p class="MsoNormal"> <p class="MsoNormal">Since it works, my questionis really more about principles: Given that each of the tables in question will contain tens of thousands of rows,is a nested join really the best way to approach this?<p class="MsoNormal"> <p class="MsoNormal">Thanks!<p class="MsoNormal">Ryan</div>
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