Re: Slow SELECT...IN statements
От | Matt Friedman |
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Тема | Re: Slow SELECT...IN statements |
Дата | |
Msg-id | 001501c0b3db$2b2504f0$03284d18@mattq3h8budilr обсуждение исходный текст |
Ответ на | Re: Slow SELECT...IN statements (Bruce Momjian <pgman@candle.pha.pa.us>) |
Ответы |
Re: Re: Slow SELECT...IN statements
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Список | pgsql-general |
I am working on a select that would use the IN statement as you can view below. After reading this thread, which says that the IN statement is "slow" I am wondering how I would rewrite using "EXISTS...IN" I've searched the docs for references to "EXISTS IN" but haven't found anything with regards to selects. Can you tell me how I can write this using "exists"? Would I reap a significant performance gain by using "exists" instead of just "in" SELECT index_uri.uri, index_uri.description, index_uri.title, index_type.type, index_type.icon, SUM(index.word_count) AS score FROM index,index_word,index_uri,index_type WHERE index_word.word IN ('radio','spry') AND index_word.word_id=index.word_id AND index_uri.uri_id = index.uri_id AND index_type.type_id = index_uri.type_id GROUP BY index_uri.uri, index_uri.description, index_uri.title, index_type.type, index.word_count, index_type.icon ORDER BY score DESC ----- Original Message ----- From: "Bruce Momjian" <pgman@candle.pha.pa.us> To: "Jan Wessely" <jawe@jawe.net> Cc: <pgsql-general@postgresql.org> Sent: Friday, March 23, 2001 9:12 AM Subject: Re: Slow SELECT...IN statements > [ Charset ISO-8859-1 unsupported, converting... ] > > The FAQ states in entry 4.23 that SELECT...IN statements are slow and > > recommends to use EXISTS...IN statements instead. It also states that this > > will be resolved in some future version. > > I didn't find any entries about that in the TODO list, does anybody know > > when this will be fixed? > > It will be fixed when we do the query tree rewrite, which is on the TODO > list, hopefully for 7.2. > > -- > Bruce Momjian | http://candle.pha.pa.us > pgman@candle.pha.pa.us | (610) 853-3000 > + If your life is a hard drive, | 830 Blythe Avenue > + Christ can be your backup. | Drexel Hill, Pennsylvania 19026 > > ---------------------------(end of broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://www.postgresql.org/search.mpl > >
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