Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
On May 6, 2010, at 4:29 PM, Merlin Moncure wrote: On Thu, May 6, 2010 at 3:23 PM, Andrew Dunstan and...@dunslane.net wrote: And many places regard select * in anything other than throw-away queries as bad practice anyway. I have seen people get bitten by it over and over again, and I have worked at companies where it is explicitly forbidden in coding standards. In terms of application queries I generally agree. However, I think this rule does not apply to server side definitions, especially in regards to views and/or composite types. There are cases where you _want_ the view to be define as 'all fields of x'...In fact, it's pretty typical IMNSHO. It may be possible to expose this behavior. I'd like to see: select * from foo -- and -- select (foo).* exhibit different behaviors -- ().* is more a type operator, returning all the fields of foo, than a field list expression. This gives us a cool loophole to exploit for views that really want to be defined with *: create view particular_foos as select (foo).* from foo where something = true; create view something_complex as select (foo).*, (func(foo.field)).*; -- execute func() just one time please! The something_complex case above is a real problem in how it behaves currently -- sometimes without a hassle free workaround. Am I off my rocker? :-) I've made this point many times (prob got annoying a long time ago) but I'm curious if you guys agree... What you're suggesting makes sense to me. What is the composite type workaround you mentioned? This is definitely an issue I face at work and would love a more elegant solution than drop and re-create the view. -- Jim C. Nasby, Database Architect j...@nasby.net 512.569.9461 (cell) http://jim.nasby.net -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
On Mon, May 17, 2010 at 2:15 PM, Jim Nasby deci...@decibel.org wrote: On May 6, 2010, at 4:29 PM, Merlin Moncure wrote: On Thu, May 6, 2010 at 3:23 PM, Andrew Dunstan and...@dunslane.net wrote: And many places regard select * in anything other than throw-away queries as bad practice anyway. I have seen people get bitten by it over and over again, and I have worked at companies where it is explicitly forbidden in coding standards. In terms of application queries I generally agree. However, I think this rule does not apply to server side definitions, especially in regards to views and/or composite types. There are cases where you _want_ the view to be define as 'all fields of x'...In fact, it's pretty typical IMNSHO. It may be possible to expose this behavior. I'd like to see: select * from foo -- and -- select (foo).* exhibit different behaviors -- ().* is more a type operator, returning all the fields of foo, than a field list expression. This gives us a cool loophole to exploit for views that really want to be defined with *: create view particular_foos as select (foo).* from foo where something = true; create view something_complex as select (foo).*, (func(foo.field)).*; -- execute func() just one time please! The something_complex case above is a real problem in how it behaves currently -- sometimes without a hassle free workaround. Am I off my rocker? :-) I've made this point many times (prob got annoying a long time ago) but I'm curious if you guys agree... What you're suggesting makes sense to me. What is the composite type workaround you mentioned? This is definitely an issue I face at work and would love a more elegant solution than drop and re-create the view. Well, the workaround I was specifically talking about was dealing with the problem of composite type return from functions executing the function multiple times: select (func()).*; This gets expanded to select func().f1, func().f2, etc. This is the behavior I think has to go. if func returns foo and foo has 6 columns, func gets executed 6 times for each row. The workaround is this: select (q).f.* from (select func() as f) q; the problem here is that forcing the function call into a subquery can be awkward in non trival queries -- it causes other problems. What you are probably looking for is to be able to add columns to a view without recreating it: create table foo(...); create view v as select foo from foo; now you can just do: select (foo).* from v; small disclaimer: I don't actually do this much, it might cause other issues. postgres is pretty smart about detecting how composite type changes cascade to other structures. This is an exception! postgres=# create table foo(a int, b int, c int); CREATE TABLE postgres=# create view v as select foo from foo; CREATE VIEW postgres=# create view vv as select (v).foo.c; CREATE VIEW postgres=# insert into foo select 1,2,3; INSERT 0 1 postgres=# insert into foo select 2,4,6; INSERT 0 1 alter table foo drop column c; -- uh oh ALTER TABLE postgres=# select * from v; -- this seems ok foo --- (1,2) (2,4) postgres=# select * from vv; -- urk! postgres=# \d+ vv View public.vv Column | Type | Modifiers | Storage | Description +-+---+-+- c | integer | | plain | View definition: SELECT (v.foo).pg.dropped.3 AS c FROM v; I don't actually mind this so much TBH...feature not bug. I hesitated fixing this because I was terrified someone might actually fix it. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
On Mon, May 17, 2010 at 2:15 PM, Jim Nasby deci...@decibel.org wrote: On May 6, 2010, at 4:29 PM, Merlin Moncure wrote: On Thu, May 6, 2010 at 3:23 PM, Andrew Dunstan and...@dunslane.net wrote: And many places regard select * in anything other than throw-away queries as bad practice anyway. I have seen people get bitten by it over and over again, and I have worked at companies where it is explicitly forbidden in coding standards. In terms of application queries I generally agree. However, I think this rule does not apply to server side definitions, especially in regards to views and/or composite types. There are cases where you _want_ the view to be define as 'all fields of x'...In fact, it's pretty typical IMNSHO. It may be possible to expose this behavior. I'd like to see: select * from foo -- and -- select (foo).* exhibit different behaviors -- ().* is more a type operator, returning all the fields of foo, than a field list expression. This gives us a cool loophole to exploit for views that really want to be defined with *: create view particular_foos as select (foo).* from foo where something = true; create view something_complex as select (foo).*, (func(foo.field)).*; -- execute func() just one time please! The something_complex case above is a real problem in how it behaves currently -- sometimes without a hassle free workaround. Am I off my rocker? :-) I've made this point many times (prob got annoying a long time ago) but I'm curious if you guys agree... What you're suggesting makes sense to me. What is the composite type workaround you mentioned? This is definitely an issue I face at work and would love a more elegant solution than drop and re-create the view. Well, the workaround I was specifically talking about was dealing with the problem of composite type return from functions executing the function multiple times: select (func()).*; This gets expanded to select func().f1, func().f2, etc. This is the behavior I think has to go. if func returns foo and foo has 6 columns, func gets executed 6 times for each row. The workaround is this: select (q).f.* from (select func() as f) q; the problem here is that forcing the function call into a subquery can be awkward in non trival queries -- it causes other problems. What you are probably looking for is to be able to add columns to a view without recreating it: create table foo(...); create view v as select foo from foo; now you can just do: select (foo).* from v; small disclaimer: I don't actually do this much, it might cause other issues. postgres is pretty smart about detecting how composite type changes cascade to other structures. This is an exception! postgres=# create table foo(a int, b int, c int); CREATE TABLE postgres=# create view v as select foo from foo; CREATE VIEW postgres=# create view vv as select (v).foo.c; CREATE VIEW postgres=# insert into foo select 1,2,3; INSERT 0 1 postgres=# insert into foo select 2,4,6; INSERT 0 1 alter table foo drop column c; -- uh oh ALTER TABLE postgres=# select * from v; -- this seems ok foo --- (1,2) (2,4) postgres=# select * from vv; -- urk! postgres=# \d+ vv View public.vv Column | Type | Modifiers | Storage | Description +-+---+-+- c | integer | | plain | View definition: SELECT (v.foo).pg.dropped.3 AS c FROM v; I don't actually mind this so much TBH...feature not bug. I hesitated fixing this because I was terrified someone might actually fix it. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
Joseph Adams joeyadams3.14...@gmail.com writes: This isn't exactly a bug, but it could be considered unintuitive behavior. It's required by the SQL standard. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
On Thu, May 6, 2010 at 3:01 PM, Joseph Adams joeyadams3.14...@gmail.com wrote: This isn't exactly a bug, but it could be considered unintuitive behavior. Consider this: by unintuitive you mean: 'explicitly defined in the SQL standard' :-). I happen to agree with you but that's irrelevant. If you absolutely require this use the composite type workaround. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
Tom Lane wrote: Joseph Adams joeyadams3.14...@gmail.com writes: This isn't exactly a bug, but it could be considered unintuitive behavior. It's required by the SQL standard. And many places regard select * in anything other than throw-away queries as bad practice anyway. I have seen people get bitten by it over and over again, and I have worked at companies where it is explicitly forbidden in coding standards. cheers andrew -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] SELECT * in a CREATE VIEW statement doesn't update column set automatically
On Thu, May 6, 2010 at 3:23 PM, Andrew Dunstan and...@dunslane.net wrote: And many places regard select * in anything other than throw-away queries as bad practice anyway. I have seen people get bitten by it over and over again, and I have worked at companies where it is explicitly forbidden in coding standards. In terms of application queries I generally agree. However, I think this rule does not apply to server side definitions, especially in regards to views and/or composite types. There are cases where you _want_ the view to be define as 'all fields of x'...In fact, it's pretty typical IMNSHO. It may be possible to expose this behavior. I'd like to see: select * from foo -- and -- select (foo).* exhibit different behaviors -- ().* is more a type operator, returning all the fields of foo, than a field list expression. This gives us a cool loophole to exploit for views that really want to be defined with *: create view particular_foos as select (foo).* from foo where something = true; create view something_complex as select (foo).*, (func(foo.field)).*; -- execute func() just one time please! The something_complex case above is a real problem in how it behaves currently -- sometimes without a hassle free workaround. Am I off my rocker? :-) I've made this point many times (prob got annoying a long time ago) but I'm curious if you guys agree... merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
