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POSelecting top n Oracle records with ROWNUM still valid in subquery?
 

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  1. POSelecting top n Oracle records with ROWNUM still valid in subquery?
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    <p>I have the following FireBird query:</p> <pre><code>update hrs h set h.plan_week_id= (select first 1 c.plan_week_id from calendar c where c.calendar_id=h.calendar_id) where coalesce(h.calendar_id,0) &lt;&gt; 0 </code></pre> <p>(Intention: For records in <code>hrs</code> with a (non-zero) <code>calendar_id</code> take <code>calendar.plan_week_id</code> and put it in <code>hrs.plan_week_id</code>)</p> <p>The trick to select the first record in Oracle is to use <a href="http://www.orafaq.com/faq/how_does_one_select_the_top_n_rows_from_a_table" rel="nofollow noreferrer">WHERE ROWNUM=1</a>, <strong>and</strong> if understand correctly <a href="https://stackoverflow.com/questions/15590215/rownum-issue-in-oracle-query">I do not have to use ROWNUM in a separate outer query because I 'only' match ROWNUM=1</a> - thanks SO for suggesting <em>Questions that may already have your answer</em> ;-)</p> <p>This would make it</p> <pre><code>update hrs h set h.plan_week_id= (select c.plan_week_id from calendar c where (c.calendar_id=h.calendar_id) and (rownum=1)) where coalesce(h.calendar_id,0) &lt;&gt; 0 </code></pre> <p>I'm actually using the 'first record' together with the selection of only <strong>one</strong> field to guarantee that I get <strong>one value</strong> back which can be put into <code>h.plan_week_id</code>.</p> <p>Question: <strong>Will the above query work under Oracle as intended?</strong></p> <p>Right now, I do not have a filled Oracle DB at hand to run the query on.</p>
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    1. USJan Doggen
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    1. CO[Here is sqlfiddle](http://sqlfiddle.com/#!4) where you could try the query.
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      1. USNick Krasnov
 

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