Re: [GENERAL] SQL - finding next date
On 11/04/2007 21:15, Jon Sime wrote: This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, Many thanks indeed to all who replied - I particularly like Jeff's solution, and will use that one. Regards, Ray. --- Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland [EMAIL PROTECTED] --- ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] SQL - finding next date
On 4/12/07, Raymond O'Donnell [EMAIL PROTECTED] wrote: On 11/04/2007 21:15, Jon Sime wrote: This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, Many thanks indeed to all who replied - I particularly like Jeff's solution, and will use that one. I think this is by far the cleanest: select * from term where start_date (select start_date from term where name = 'foo') order by start_date limit 1; merlin ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] SQL - finding next date
On 4/12/07, Merlin Moncure [EMAIL PROTECTED] wrote: On 4/12/07, Raymond O'Donnell [EMAIL PROTECTED] wrote: On 11/04/2007 21:15, Jon Sime wrote: This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, Many thanks indeed to all who replied - I particularly like Jeff's solution, and will use that one. I think this is by far the cleanest: select * from term where start_date (select start_date from term where name = 'foo') order by start_date limit 1; just to clarify, that would be the best way to pick out the next term from a known term. If you wanted to present the complete list of terms along with the next sequential term, I would suggest: select name, (select name from term f where e.start_date f.start_date order by f.start_date limit 1) as next_term from term e; I tested it and this is much faster than 'where exists' solution. If you want all the properties of the next term, just replace 'select name' with 'select term' which will return the term as a record object. merlin ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] SQL - finding next date
On 12/04/2007 18:01, Merlin Moncure wrote: I tested it and this is much faster than 'where exists' solution. Is this an attribute of PostgreSQL in particular, or would it be true of RDBMSs in general? Thanks again, Ray. --- Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland [EMAIL PROTECTED] --- ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] SQL - finding next date
On 4/12/07, Raymond O'Donnell [EMAIL PROTECTED] wrote: On 12/04/2007 18:01, Merlin Moncure wrote: I tested it and this is much faster than 'where exists' solution. Is this an attribute of PostgreSQL in particular, or would it be true of RDBMSs in general? evaluation of subqueries is one place where various databases quite a lot...postgresql one of the nice things about postgresql is that sql optimization usually (but not always) entails finding the most direct query to attack the problem. other databases might prefer joins or standard subquery approach (where in/exists, etc). my suggestion to return the record in a field as a composite type is a non-standard trick (i think...do composite types exist in the sql standard?). merlin ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [GENERAL] SQL - finding next date
Merlin Moncure escribió: my suggestion to return the record in a field as a composite type is a non-standard trick (i think...do composite types exist in the sql standard?). I think composite types are in the standard, yes, but they are a bit different from what we have. I tried to read that part of the standard a while back and came up blank, it's too filled with strange constructs. Too closely linked to tables for one thing; there seems to be no notion of anonymous or standalone types. -- Alvaro Herrerahttp://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] SQL - finding next date
On 4/11/07, Raymond O'Donnell [EMAIL PROTECTED] wrote: Hi all, This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, and I need an SQL query such that for any given term I want to find the next term by starting date (or just NULL if there isn't one). Here's the table - CREATE TABLE terms ( term_id serial NOT NULL, term_name character varying(40) NOT NULL, term_starts date NOT NULL, term_ends date NOT NULL, . ) - so, supposing I have the following data - term_id | term_name | term_starts | ... -+-+-+-- 1 | Spring 2007 | 2007-01-10 | ... 2 | Autumn 2007 | 2007-09-01 | ... 6 | Spring 2008 | 2008-01-06 | ... - then for term '1' I'd like to return '2', for term '2' I'd like to return '6', and so on. The closest I've got is getting ALL terms that start after a given one, but I run into trouble after thatany help will be appreciated! Thanks in advance, Ray. --- Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland [EMAIL PROTECTED] --- SELECT main.term_name, main.term_starts mts, next.term_name, next.term_starts nts FROM terms main LEFT JOIN terms NEXT ON main.term_starts NEXT.term_starts WHERE NOT EXISTS (SELECT 1 FROM terms t WHERE t.term_starts main.term_starts AND t.term_starts NEXT.term_starts) It's kind of a sneak attack way of getting at the min(term_starts) without using an aggregate. Jeff
[GENERAL] SQL - finding next date
Hi all, This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, and I need an SQL query such that for any given term I want to find the next term by starting date (or just NULL if there isn't one). Here's the table - CREATE TABLE terms ( term_id serial NOT NULL, term_name character varying(40) NOT NULL, term_starts date NOT NULL, term_ends date NOT NULL, . ) - so, supposing I have the following data - term_id | term_name | term_starts | ... -+-+-+-- 1 | Spring 2007 | 2007-01-10 | ... 2 | Autumn 2007 | 2007-09-01 | ... 6 | Spring 2008 | 2008-01-06 | ... - then for term '1' I'd like to return '2', for term '2' I'd like to return '6', and so on. The closest I've got is getting ALL terms that start after a given one, but I run into trouble after thatany help will be appreciated! Thanks in advance, Ray. --- Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland [EMAIL PROTECTED] --- ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] SQL - finding next date
On 4/11/07, Raymond O'Donnell [EMAIL PROTECTED] wrote: Hi all, This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, and I need an SQL query such that for any given term I want to find the next term by starting date (or just NULL if there isn't one). Here's the table - CREATE TABLE terms ( term_id serial NOT NULL, term_name character varying(40) NOT NULL, term_starts date NOT NULL, term_ends date NOT NULL, . ) - so, supposing I have the following data - term_id | term_name | term_starts | ... -+-+-+-- 1 | Spring 2007 | 2007-01-10 | ... 2 | Autumn 2007 | 2007-09-01 | ... 6 | Spring 2008 | 2008-01-06 | ... - then for term '1' I'd like to return '2', for term '2' I'd like to return '6', and so on. The closest I've got is getting ALL terms that start after a given one, but I run into trouble after thatany help will be appreciated! Thanks in advance, Ray. --- Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland [EMAIL PROTECTED] --- SELECT main.term_name, main.term_starts mts, next.term_name, next.term_starts nts FROM terms main LEFT JOIN terms NEXT ON main.term_starts NEXT.term_starts WHERE NOT EXISTS (SELECT 1 FROM terms t WHERE t.term_starts main.term_starts AND t.term_starts NEXT.term_starts) It's kind of a sneak attack way of getting at the min(term_starts) without using an aggregate. Jeff
Re: [GENERAL] SQL - finding next date
You'll need to do something like this, called a correlated subquery: Select t1.term_id, t1.term_name, t1.term_starts, t2.term_id as next_term From term t1, term t2 where t2.term_starts = (select min(t3.term_starts) from term t3 where t3.term_starts t1.term_starts) -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Raymond O'Donnell Sent: Wednesday, April 11, 2007 3:40 PM To: 'PostgreSQL' Subject: [GENERAL] SQL - finding next date Hi all, This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, and I need an SQL query such that for any given term I want to find the next term by starting date (or just NULL if there isn't one). Here's the table - CREATE TABLE terms ( term_id serial NOT NULL, term_name character varying(40) NOT NULL, term_starts date NOT NULL, term_ends date NOT NULL, . ) - so, supposing I have the following data - term_id | term_name | term_starts | ... -+-+-+-- 1 | Spring 2007 | 2007-01-10 | ... 2 | Autumn 2007 | 2007-09-01 | ... 6 | Spring 2008 | 2008-01-06 | ... - then for term '1' I'd like to return '2', for term '2' I'd like to return '6', and so on. The closest I've got is getting ALL terms that start after a given one, but I run into trouble after thatany help will be appreciated! Thanks in advance, Ray. --- Raymond O'Donnell, Director of Music, Galway Cathedral, Ireland [EMAIL PROTECTED] --- ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] SQL - finding next date
Raymond O'Donnell wrote: This is probably a very simple one, but I just can't see the answer and it's driving me nuts. I have a table holding details of academic terms, and I need an SQL query such that for any given term I want to find the next term by starting date (or just NULL if there isn't one). Here's one approach given your table def. select t.*, ( select term_id from terms where term_starts t.term_ends order by term_starts asc limit 1 ) as next_term_id from terms t order by t.term_starts asc; -Jon -- Senior Systems Developer Media Matters for America http://mediamatters.org/ ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
