ROW_NUMBER alias
От | Robins |
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Тема | ROW_NUMBER alias |
Дата | |
Msg-id | 36af4bed0705060901s36fed269ye5a8588eaffbd750@mail.gmail.com обсуждение исходный текст |
Ответы |
Re: ROW_NUMBER alias
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Список | pgsql-sql |
Hi,<br /><br />I needed ROW_NUMBER() in PostGresql and I did find the 'temporary sequence' method as a workaround and i thinkit at least gets the job done relatively well, ... so no problems there. <br /><br />Its just that from a usabilitypoint of view, isn't it better that we provide some kind of an aliasing mechanism here that allows a new user to(unknowingly but) implicitly use a temporary sequence rather than make him use SubQuery with a COUNT(*) and a comparisonoperator (with disastrous performance) instead ?? <br /><br />So for a new user :<br /><br />A query such as this:<br /><br /> SELECT ROW_NUMBER() AS row_number , a, b, c<br /> FROM table<br /> WHERE table_id = 973<br/> ORDER BY record_date;<br /><br />is internally interpreted by the planner as : <br /><br /> CREATE TEMPSEQUENCE rownum; <br /><br /> SELECT nextval('rownum') AS row_number , t.a, t.b, t.c<br /> FROM (<br /> SELECT a, b, c<br /> FROM table<br /> WHERE table_id = 973<br /> ORDER BY record_date<br /> )t;<br /><br /> DROP SEQUENCE rownum;<br /><br /> <br clear="all" />Any ideas ?<br />(Of what I remember, I think tillrecently PostgreSql internally replaced 'MAX(x)' queries with a 'ORDER BY x DESC LIMIT 1' implicitly)<br /><br />--<br/>Robins
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