Re: [GENERAL] Cast SRF returning record to a table type?
On Sat, Apr 18, 2015 at 5:37 PM, Jim Nasby jim.na...@bluetreble.com wrote:
On 4/18/15 12:47 AM, David G. Johnston wrote:
If you could find a way to pass a value of type some_table into the
function - instead of the name/text 'some_table‘ - you could possibly
use polymorphic pseudotypes...just imagining here...
Oh, I didn't think about that. Maybe I'll try it.
What I ended up with is this:
CREATE FUNCTION ... (
) RETURNS SETOF text ...
...
RETURN QUERY EXECUTE format(
'SELECT row(t.*)::text FROM %I.%I AS t'
, ...
);
So the function is getting a record and casting it to text. To call the
function you have to...
SELECT (function(...))::name_of_table).*
*do not do this*. If table has three fields a,b,c, the query will expand to:
SELECT function(...).a, function(...).b, function(...).c;
SRF in column list (now that we have LATERAL) can now be considered a
'bad practice' in most cases I can think of (possibly exempting
trivial data productions with generate_series, etc).
that gives you the same output as if you'd selected directly from the table.
I think the following is better:
postgres=# create table foo(id int, b text);
CREATE TABLE
postgres=# insert into foo select s, s || '_test' from generate_series(1,3) s;
INSERT 0 3
create or replace function getdata(r anyelement, tablename text)
returns setof anyelement as
$$
begin
return query execute format('select * from %s', quote_ident(tablename));
end;
$$ language plpgsql;
CREATE FUNCTION
postgres=# select * from getdata(null::foo, 'foo');
id │ b
┼
1 │ 1_test
2 │ 2_test
3 │ 3_test
(3 rows)
merlin
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Re: [GENERAL] Cast SRF returning record to a table type?
On Mon, Apr 20, 2015 at 7:57 AM, Merlin Moncure mmonc...@gmail.com wrote:
On Sat, Apr 18, 2015 at 5:37 PM, Jim Nasby jim.na...@bluetreble.com
wrote:
On 4/18/15 12:47 AM, David G. Johnston wrote:
If you could find a way to pass a value of type some_table into the
function - instead of the name/text 'some_table‘ - you could possibly
use polymorphic pseudotypes...just imagining here...
Oh, I didn't think about that. Maybe I'll try it.
What I ended up with is this:
CREATE FUNCTION ... (
) RETURNS SETOF text ...
...
RETURN QUERY EXECUTE format(
'SELECT row(t.*)::text FROM %I.%I AS t'
, ...
);
So the function is getting a record and casting it to text. To call the
function you have to...
SELECT (function(...))::name_of_table).*
*do not do this*. If table has three fields a,b,c, the query will expand
to:
SELECT function(...).a, function(...).b, function(...).c;
SRF in column list (now that we have LATERAL) can now be considered a
'bad practice' in most cases I can think of (possibly exempting
trivial data productions with generate_series, etc).
that gives you the same output as if you'd selected directly from the
table.
I think the following is better:
postgres=# create table foo(id int, b text);
CREATE TABLE
postgres=# insert into foo select s, s || '_test' from
generate_series(1,3) s;
INSERT 0 3
create or replace function getdata(r anyelement, tablename text)
returns setof anyelement as
$$
begin
return query execute format('select * from %s', quote_ident(tablename));
end;
$$ language plpgsql;
CREATE FUNCTION
postgres=# select * from getdata(null::foo, 'foo');
id │ b
┼
1 │ 1_test
2 │ 2_test
3 │ 3_test
(3 rows)
Any particular reason you wouldn't write the function this way?
create or replace function getdata(r anyelement)
returns setof anyelement as
$$
begin
return query execute format('select * from %I', pg_typeof(r));
end;
$$ language plpgsql;
Specifically, using pg_typeof(r) instead of passing in the table name
twice; and using %I instead of %s + quote_ident(...)
Replacing the above function still provides the same results.
Agreed this really wants to called in the FROM clause.
David J.
Re: [GENERAL] Cast SRF returning record to a table type?
On Mon, Apr 20, 2015 at 9:40 AM, David G. Johnston
david.g.johns...@gmail.com wrote:
On Mon, Apr 20, 2015 at 7:57 AM, Merlin Moncure mmonc...@gmail.com
wrote:
On Sat, Apr 18, 2015 at 5:37 PM, Jim Nasby jim.na...@bluetreble.com
wrote:
On 4/18/15 12:47 AM, David G. Johnston wrote:
If you could find a way to pass a value of type some_table into the
function - instead of the name/text 'some_table‘ - you could possibly
use polymorphic pseudotypes...just imagining here...
Oh, I didn't think about that. Maybe I'll try it.
What I ended up with is this:
CREATE FUNCTION ... (
) RETURNS SETOF text ...
...
RETURN QUERY EXECUTE format(
'SELECT row(t.*)::text FROM %I.%I AS t'
, ...
);
So the function is getting a record and casting it to text. To call the
function you have to...
SELECT (function(...))::name_of_table).*
*do not do this*. If table has three fields a,b,c, the query will expand
to:
SELECT function(...).a, function(...).b, function(...).c;
SRF in column list (now that we have LATERAL) can now be considered a
'bad practice' in most cases I can think of (possibly exempting
trivial data productions with generate_series, etc).
that gives you the same output as if you'd selected directly from the
table.
I think the following is better:
postgres=# create table foo(id int, b text);
CREATE TABLE
postgres=# insert into foo select s, s || '_test' from
generate_series(1,3) s;
INSERT 0 3
create or replace function getdata(r anyelement, tablename text)
returns setof anyelement as
$$
begin
return query execute format('select * from %s', quote_ident(tablename));
end;
$$ language plpgsql;
CREATE FUNCTION
postgres=# select * from getdata(null::foo, 'foo');
id │ b
┼
1 │ 1_test
2 │ 2_test
3 │ 3_test
(3 rows)
Any particular reason you wouldn't write the function this way?
create or replace function getdata(r anyelement)
returns setof anyelement as
$$
begin
return query execute format('select * from %I', pg_typeof(r));
end;
$$ language plpgsql;
Specifically, using pg_typeof(r) instead of passing in the table name
twice; and using %I instead of %s + quote_ident(...)
Replacing the above function still provides the same results.
Agreed this really wants to called in the FROM clause.
David J.
FWIW - I was inspired by Java's Generics handling for coming up with
this possibility.
David J.
Re: [GENERAL] Cast SRF returning record to a table type?
On Mon, Apr 20, 2015 at 11:40 AM, David G. Johnston
david.g.johns...@gmail.com wrote:
On Mon, Apr 20, 2015 at 7:57 AM, Merlin Moncure mmonc...@gmail.com wrote:
On Sat, Apr 18, 2015 at 5:37 PM, Jim Nasby jim.na...@bluetreble.com
wrote:
On 4/18/15 12:47 AM, David G. Johnston wrote:
If you could find a way to pass a value of type some_table into the
function - instead of the name/text 'some_table‘ - you could possibly
use polymorphic pseudotypes...just imagining here...
Oh, I didn't think about that. Maybe I'll try it.
What I ended up with is this:
CREATE FUNCTION ... (
) RETURNS SETOF text ...
...
RETURN QUERY EXECUTE format(
'SELECT row(t.*)::text FROM %I.%I AS t'
, ...
);
So the function is getting a record and casting it to text. To call the
function you have to...
SELECT (function(...))::name_of_table).*
*do not do this*. If table has three fields a,b,c, the query will expand
to:
SELECT function(...).a, function(...).b, function(...).c;
SRF in column list (now that we have LATERAL) can now be considered a
'bad practice' in most cases I can think of (possibly exempting
trivial data productions with generate_series, etc).
that gives you the same output as if you'd selected directly from the
table.
I think the following is better:
postgres=# create table foo(id int, b text);
CREATE TABLE
postgres=# insert into foo select s, s || '_test' from
generate_series(1,3) s;
INSERT 0 3
create or replace function getdata(r anyelement, tablename text)
returns setof anyelement as
$$
begin
return query execute format('select * from %s', quote_ident(tablename));
end;
$$ language plpgsql;
CREATE FUNCTION
postgres=# select * from getdata(null::foo, 'foo');
id │ b
┼
1 │ 1_test
2 │ 2_test
3 │ 3_test
(3 rows)
Any particular reason you wouldn't write the function this way?
create or replace function getdata(r anyelement)
none at all: this is better since pg_typeof() automatically
quote_idents (something which I did not know but verified!).
merlin
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Re: [GENERAL] Cast SRF returning record to a table type?
On 4/18/15 12:47 AM, David G. Johnston wrote: If you could find a way to pass a value of type some_table into the function - instead of the name/text 'some_table‘ - you could possibly use polymorphic pseudotypes...just imagining here... Oh, I didn't think about that. Maybe I'll try it. What I ended up with is this: CREATE FUNCTION ... ( ) RETURNS SETOF text ... ... RETURN QUERY EXECUTE format( 'SELECT row(t.*)::text FROM %I.%I AS t' , ... ); So the function is getting a record and casting it to text. To call the function you have to... SELECT (function(...))::name_of_table).* that gives you the same output as if you'd selected directly from the table. -- Jim Nasby, Data Architect, Blue Treble Consulting Data in Trouble? Get it in Treble! http://BlueTreble.com -- 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] Cast SRF returning record to a table type?
On 4/17/15 7:39 PM, David G. Johnston wrote: On Friday, April 17, 2015, Jim Nasby jim.na...@bluetreble.com mailto:jim.na...@bluetreble.com wrote: I'm working on a function that will return a set of test data, for unit testing database stuff. It does a few things, but ultimately returns SETOF record that's essentially: RETURN QUERY EXECUTE 'SELECT * FROM ' || table_name; Because it's always going to return a real relation, I'd like to be able to the equivalent of: SELECT ... FROM my_function( 'some_table' )::some_table; Unfortunately this means cast the existing type to some_table and record is not a valid type in this context. Is there any trick that would allow that to work? I know that instead of 'SELECT * ...' I can do 'SELECT row(t.*) FROM ' || table_name || ' AS t' and then do SELECT ... FROM my_function( 'some_table' ) AS data( d some_table ) but I'm hoping to avoid the extra level of indirection. Haven't explored this specific code in depth...but which part - the function alias or the select row(t.*)? They seem to be independent concerns. I'm saying that I know I can use the row construct as a poor work-around. What I actually want though is a way to tell this query: SELECT ... FROM my_function( 'some_table' ) that my_function is returning a record that exactly matches my_table. I suspect there's not actually any way to do that :( -- Jim Nasby, Data Architect, Blue Treble Consulting Data in Trouble? Get it in Treble! http://BlueTreble.com -- 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] Cast SRF returning record to a table type?
On Friday, April 17, 2015, Jim Nasby jim.na...@bluetreble.com wrote:
On 4/17/15 7:39 PM, David G. Johnston wrote:
On Friday, April 17, 2015, Jim Nasby jim.na...@bluetreble.com
mailto:jim.na...@bluetreble.com wrote:
I'm working on a function that will return a set of test data, for
unit testing database stuff. It does a few things, but ultimately
returns SETOF record that's essentially:
RETURN QUERY EXECUTE 'SELECT * FROM ' || table_name;
Because it's always going to return a real relation, I'd like to be
able to the equivalent of:
SELECT ... FROM my_function( 'some_table' )::some_table;
Unfortunately this means cast the existing type to some_table and
record is not a valid type in this context.
Is there any trick that would allow that to work? I know that
instead of 'SELECT * ...' I can do 'SELECT row(t.*) FROM ' ||
table_name || ' AS t' and then do
SELECT ... FROM my_function( 'some_table' ) AS data( d some_table )
but I'm hoping to avoid the extra level of indirection.
Haven't explored this specific code in depth...but which part - the
function alias or the select row(t.*)? They seem to be independent
concerns.
I'm saying that I know I can use the row construct as a poor work-around.
What I actually want though is a way to tell this query:
SELECT ... FROM my_function( 'some_table' )
that my_function is returning a record that exactly matches my_table. I
suspect there's not actually any way to do that :(
No matter what you do inside the function you have to write that last query
as from my_function('some_table') AS (rel some_table) otherwise the
planer is clueless. You cannot defer the type until runtime. Your cast
form is slightly more succinct but I cannot see making it work when the
current method is serviceable.
Inside the function I would have thought that select * shoud work - no need
to use the row(t.*) construct - but the later seems reasonably direct...
If you could find a way to pass a value of type some_table into the
function - instead of the name/text 'some_table‘ - you could possibly use
polymorphic pseudotypes...just imagining here...
Select ... From my_func(null::some_table)
Create function my_func(tbl any) returns setof any
Use typeof to get a text string of the tbl arg's type.
You could maybe also return a refcursor...
David J.
[GENERAL] Cast SRF returning record to a table type?
I'm working on a function that will return a set of test data, for unit testing database stuff. It does a few things, but ultimately returns SETOF record that's essentially: RETURN QUERY EXECUTE 'SELECT * FROM ' || table_name; Because it's always going to return a real relation, I'd like to be able to the equivalent of: SELECT ... FROM my_function( 'some_table' )::some_table; Is there any trick that would allow that to work? I know that instead of 'SELECT * ...' I can do 'SELECT row(t.*) FROM ' || table_name || ' AS t' and then do SELECT ... FROM my_function( 'some_table' ) AS data( d some_table ) but I'm hoping to avoid the extra level of indirection. -- Jim Nasby, Data Architect, Blue Treble Consulting Data in Trouble? Get it in Treble! http://BlueTreble.com -- 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] Cast SRF returning record to a table type?
On Friday, April 17, 2015, Jim Nasby jim.na...@bluetreble.com wrote: I'm working on a function that will return a set of test data, for unit testing database stuff. It does a few things, but ultimately returns SETOF record that's essentially: RETURN QUERY EXECUTE 'SELECT * FROM ' || table_name; Because it's always going to return a real relation, I'd like to be able to the equivalent of: SELECT ... FROM my_function( 'some_table' )::some_table; Unfortunately this means cast the existing type to some_table and record is not a valid type in this context. Is there any trick that would allow that to work? I know that instead of 'SELECT * ...' I can do 'SELECT row(t.*) FROM ' || table_name || ' AS t' and then do SELECT ... FROM my_function( 'some_table' ) AS data( d some_table ) but I'm hoping to avoid the extra level of indirection. Haven't explored this specific code in depth...but which part - the function alias or the select row(t.*)? They seem to be independent concerns. David J.
