RE: Index on substring?
От | Jeff Eckermann |
---|---|
Тема | RE: Index on substring? |
Дата | |
Msg-id | 08CD1781F85AD4118E0800A0C9B8580B09472E@NEZU обсуждение исходный текст |
Ответ на | Index on substring? (Jeff Eckermann <jeckermann@verio.net>) |
Список | pgsql-general |
Tom, Thanks very much for your full and clear answer. It's hard to imagine a general use for this facility, anyway. For me this is a one-off exercise, albeit a big one. Regards > -----Original Message----- > From: Tom Lane [SMTP:tgl@sss.pgh.pa.us] > Sent: Thursday, October 12, 2000 12:49 AM > To: Jeff Eckermann > Cc: 'pgsql-general@postgresql.org' > Subject: Re: [GENERAL] Index on substring? > > Jeff Eckermann <jeckermann@verio.net> writes: > > extracts=# create index c_namesum_i on customers > (substr(bill_company,1,5)); > > ERROR: parser: parse error at or near "1" > > The functional-index syntax only allows a function name applied to > simple column names. > > You can work around this by defining a function that handles any > additional computation needed, eg, > > create index c_namesum_i on customers (mysubstr15(bill_company)); > > where mysubstr15(foo) returns substr(foo,1,5). In current releases > the intermediate function has to be in C or a PL language. 7.1 will > allow a SQL-language function too (although frankly I'd recommend > against using a SQL function for indexing, on performance grounds). > > There's been some talk of generalizing the functional-index support > into arbitrary-expression-index support, but it doesn't seem to be > real high on anyone's priority list. > > regards, tom lane
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