Re: [GENERAL] Short-circuit boolean evaluation
On 2011-04-30, Jon Smark wrote: > Hi, > > Does Postgresql perform short-circuit boolean evaluation both in SQL > and PL/pgSQL functions? sometimes. the planner will rearrange what you write, for this reason it is very likely that > SELECT count(*) FROM foobar WHERE foobar.id = $1 AND do_stuff (foobar.name); will perform as well as SELECT count(*) FROM foobar WHERE do_stuff (foobar.name) and foobar.id = $1; because the planner will rewrite this 'bad version' to execute the same as the good version. If you have an index on foobar.id or on do_stuff(foobar.name) or on both it might be used to speed up the query. You can give the planner a hint as to how expensive each function is when you define the function. in general the planner will take care of it for you if you want to control when the function gets called with a boolean test consider using case. -- ⚂⚃ 100% natural -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Short-circuit boolean evaluation
David Johnston writes: > No. It will not be called > Or > No. Postgresql does not short-circuit boolean evaluations > ? The correct answer is "maybe". See http://www.postgresql.org/docs/9.0/static/sql-expressions.html#SYNTAX-EXPRESS-EVAL regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Short-circuit boolean evaluation
On Sat, Apr 30, 2011 at 10:34:32AM -0400, David Johnston wrote: > No. It will not be called > Or > No. Postgresql does not short-circuit boolean evaluations > ? SQL is a somewhat declarative language. There is no "order" to evaluation as such. So you can't talk about short circuiting either. This applies to any SQL database. You can somewhat enforce order with subselects and CASE and other such constructs. Have a nice day, -- Martijn van Oosterhout http://svana.org/kleptog/ > Patriotism is when love of your own people comes first; nationalism, > when hate for people other than your own comes first. > - Charles de Gaulle signature.asc Description: Digital signature
Re: [GENERAL] Short-circuit boolean evaluation
No. It will not be called Or No. Postgresql does not short-circuit boolean evaluations ? On Apr 30, 2011, at 10:27, pasman pasmański wrote: > No. > > 2011/4/30, Jon Smark : >> Hi, >> >> Does Postgresql perform short-circuit boolean evaluation both in SQL >> and PL/pgSQL functions? As an example, suppose I have a function called >> "do_stuff" which is computationally intensive. In the example below, >> will it be called for rows for which the first predicate (foobar.id = $1) >> is false? >> >> SELECT count(*) FROM foobar WHERE foobar.id = $1 AND do_stuff (foobar.name); >> >> Thanks! >> Jon >> >> >> -- >> Sent via pgsql-general mailing list (pgsql-general@postgresql.org) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-general >> > > > -- > > pasman > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Short-circuit boolean evaluation
No. 2011/4/30, Jon Smark : > Hi, > > Does Postgresql perform short-circuit boolean evaluation both in SQL > and PL/pgSQL functions? As an example, suppose I have a function called > "do_stuff" which is computationally intensive. In the example below, > will it be called for rows for which the first predicate (foobar.id = $1) > is false? > > SELECT count(*) FROM foobar WHERE foobar.id = $1 AND do_stuff (foobar.name); > > Thanks! > Jon > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general > -- pasman -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
[GENERAL] Short-circuit boolean evaluation
Hi, Does Postgresql perform short-circuit boolean evaluation both in SQL and PL/pgSQL functions? As an example, suppose I have a function called "do_stuff" which is computationally intensive. In the example below, will it be called for rows for which the first predicate (foobar.id = $1) is false? SELECT count(*) FROM foobar WHERE foobar.id = $1 AND do_stuff (foobar.name); Thanks! Jon -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
