I there, I am new to PL/pgSQL, the project I am working on started using it for some data-intensive handling implementations, I am failing to understand some basic foundations, even reviewing the docs again and again
So I have a function that looks like this:
CREATE OR REPLACE FUNCTION sum_stuff_over_value(
param1 uuid,
param2 uuid,
param3 enum
)
RETURNS float AS
$$
DECLARE
table_name varchar;
column_name varchar;
resolution integer;
another_table varchar := 'name_of_another_table';
another_column varchar := 'name_of_another_column';
sum float;
BEGIN
-- Get data from another table fiven a param2 ID
SELECT * INTO table_name, column_name, esolution
FROM get_table_and_column_by_Id(param2, param3);
-- Sum table column over region
EXECUTE format(
'SELECT sum(grid_mat.%I * grid_def.%I)
FROM
get_uncompact_region($1, $2) region
INNER JOIN %I grid_mat ON grid_mat.index = region.index
INNER JOIN %I grid_def ON grid_def.index = region.index;
', column_name, another_column, table_name, another_table)
USING param1, resolution
INTO sum;
RETURN sum;
END;
$$
LANGUAGE plpgsql;
I'd say I fairly understand the very very basic flow, instantiate vars, some of them assigned, etc...
What I am struggling the most is understanding which value holds %I, and how here
INNER JOIN %I grid_mat ON grid_mat.index = region.index
INNER JOIN %I grid_def ON grid_def.index = region.index;
%I is holding (I believe) different values to join different tables
I tried to figure it out by raising notices to print values, but I couldn't make it work. I am trying to add some breakpoints to debug this isolated in the DB but as it's new to me is not being straightforward
Can anyone help me understand what is going on here?
Thanks a lot in advance
You should read the documentation of format. The first %I will be replaced by the value of the second argument of format (column_name), escaped as an identifier, the second %I will be replaced by the value of another_column, and so on.
FROM https://www.postgresql.org/docs/14/plpgsql-statements.html#PLPGSQL-STATEMENTS-SQL-ONEROW.
around section: Example 43.1. Quoting Values in Dynamic Queries
quote:
Dynamic SQL statements can also be safely constructed using the format function (see Section 9.4.1). For example:
EXECUTE format('UPDATE tbl SET %I = %L '
'WHERE key = %L', colname, newvalue, keyvalue);
Section 9.4.1 LINK: :
https://www.postgresql.org/docs/14/functions-string.html#FUNCTIONS-STRING-FORMAT
Quote from Section 9.4.1
type (required) The type of format conversion to use to produce the
format specifier's output. The following types are supported:
s formats the argument value as a simple string. A null value is
treated as an empty string.
I treats the argument value as an SQL identifier, double-quoting it if
necessary. It is an error for the value to be null (equivalent to
quote_ident).
L quotes the argument value as an SQL literal. A null value is
displayed as the string NULL, without quotes (equivalent to
quote_nullable).
There have serval examples, quote:
SELECT format('INSERT INTO %I VALUES(%L)', 'Foo bar', E'O\'Reilly');
Result: INSERT INTO "Foo bar" VALUES('O''Reilly')
Finally explain:
your EXECUTE format string have 4 %I. Then
1st %I refer to column_name
2nd %I refer to another_column
3rd %I refer to table_name
4th %I refer to another_table
Related
begin;
create type public.ltree as (a int, b int);
create table public.parent_tree(parent_id int,l_tree ltree);
insert into public.parent_tree values(1,(2,2)),(2,(1,2)),(3, (1,28));
commit;
Trying to replicate the solution in this answer:
Format specifier for integer variables in format() for EXECUTE?
For a function with composite type:
CREATE OR REPLACE FUNCTION public.get_parent_ltree
(_parent_id int, tbl_name regclass , OUT _l_tree ltree)
LANGUAGE plpgsql AS
$func$
BEGIN
EXECUTE format('SELECT l_tree FROM %s WHERE parent_id = $1', tbl_name)
INTO _l_tree
USING _parent_id;
END
$func$;
The effective query executed:
select l_tree from parent_tree where parent_id = 1;
Executing the function:
select get_parent_ltree(1,'parent_tree');
select get_parent_ltree(1,'public.parent_tree');
I get this error:
ERROR: invalid input syntax for type integer: "(2,2)"
CONTEXT: PL/pgSQL function get_parent_ltree(integer,regclass) line 3 at EXECUTE
Context of line 3:
The output parameter _l_tree is a "row variable". (A composite type is treated as row variable.) SELECT INTO assigns fields of a row variable one-by-one. The manual:
The optional target is a record variable, a row variable, or a comma-separated list of simple variables and record/row fields, [...]
So, currently (pg 14), a row or record variables must stand alone as target. Or as the according Postgres error message would put it:
ERROR: record variable cannot be part of multiple-item INTO list
This works:
CREATE OR REPLACE FUNCTION public.get_parent_ltree (IN _parent_id int
, IN _tbl_name regclass
, OUT _l_tree ltree)
LANGUAGE plpgsql AS
$func$
BEGIN
EXECUTE format('SELECT (l_tree).* FROM %s WHERE parent_id = $1', _tbl_name)
INTO _l_tree
USING _parent_id;
END
$func$;
Or this:
CREATE OR REPLACE FUNCTION public.get_parent_ltree2 (IN _parent_id int
, IN _tbl_name regclass
, OUT _l_tree ltree)
LANGUAGE plpgsql AS
$func$
BEGIN
EXECUTE format('SELECT (l_tree).a, (l_tree).b FROM %s WHERE parent_id = $1', _tbl_name)
INTO _l_tree.a, _l_tree.b
USING _parent_id;
END
$func$;
db<>fiddle here
I agree that this is rather tricky. One might expect that a composite field is treated as a single field (like a simple type). But that's currently not so in PL/pgSQL assignments.
A related quote from the manual about composite types:
A composite type represents the structure of a row or record; it is
essentially just a list of field names and their data types.
PostgreSQL allows composite types to be used in many of the same ways that simple types can be used.
Bold emphasis mine.
Many. Not all.
Related:
Use of custom return types in a FOR loop in plpgsql
PostgreSQL: ERROR: 42601: a column definition list is required for functions returning "record"
Aside: Consider the additional module ltree instead of "growing your own". And if you continue working with your own composite type, consider a different name to avoid confusion / conflict with that module.
It looks like a Postgres bug but Erwin clarifies the issue in the adjacent answer. One of the natural workarounds is to use an auxiliary text variable in the way like this:
create or replace function get_parent_ltree(_parent_id int, tbl_name regclass)
returns ltree language plpgsql as
$func$
declare
rslt text;
begin
execute format('select l_tree from %s where parent_id = $1', tbl_name)
into rslt
using _parent_id;
return rslt::ltree;
end
$func$;
I have a fields table to store column information for other tables:
CREATE TABLE public.fields (
schema_name varchar(100),
table_name varchar(100),
column_text varchar(100),
column_name varchar(100),
column_type varchar(100) default 'varchar(100)',
column_visible boolean
);
And I'd like to create a function to fetch data for a specific table.
Just tried sth like this:
create or replace function public.get_table(schema_name text,
table_name text,
active boolean default true)
returns setof record as $$
declare
entity_name text default schema_name || '.' || table_name;
r record;
begin
for r in EXECUTE 'select * from ' || entity_name loop
return next r;
end loop;
return;
end
$$
language plpgsql;
With this function I have to specify columns when I call it!
select * from public.get_table('public', 'users') as dept(id int, uname text);
I want to pass schema_name and table_name as parameters to function and get record list, according to column_visible field in public.fields table.
Solution for the simple case
As explained in the referenced answers below, you can use registered (row) types, and thus implicitly declare the return type of a polymorphic function:
CREATE OR REPLACE FUNCTION public.get_table(_tbl_type anyelement)
RETURNS SETOF anyelement AS
$func$
BEGIN
RETURN QUERY EXECUTE format('TABLE %s', pg_typeof(_tbl_type));
END
$func$ LANGUAGE plpgsql;
Call:
SELECT * FROM public.get_table(NULL::public.users); -- note the syntax!
Returns the complete table (with all user columns).
Wait! How?
Detailed explanation in this related answer, chapter
"Various complete table types":
Refactor a PL/pgSQL function to return the output of various SELECT queries
TABLE foo is just short for SELECT * FROM foo:
Is there a shortcut for SELECT * FROM?
2 steps for completely dynamic return type
But what you are trying to do is strictly impossible in a single SQL command.
I want to pass schema_name and table_name as parameters to function and get record list, according to column_visible field in
public.fields table.
There is no direct way to return an arbitrary selection of columns (return type not known at call time) from a function - or any SQL command. SQL demands to know number, names and types of resulting columns at call time. More in the 2nd chapter of this related answer:
How do I generate a pivoted CROSS JOIN where the resulting table definition is unknown?
There are various workarounds. You could wrap the result in one of the standard document types (json, jsonb, hstore, xml).
Or you generate the query with one function call and execute the result with the next:
CREATE OR REPLACE FUNCTION public.generate_get_table(_schema_name text, _table_name text)
RETURNS text AS
$func$
SELECT format('SELECT %s FROM %I.%I'
, string_agg(quote_ident(column_name), ', ')
, schema_name
, table_name)
FROM fields
WHERE column_visible
AND schema_name = _schema_name
AND table_name = _table_name
GROUP BY schema_name, table_name
ORDER BY schema_name, table_name;
$func$ LANGUAGE sql;
Call:
SELECT public.generate_get_table('public', 'users');
This create a query of the form:
SELECT usr_id, usr FROM public.users;
Execute it in the 2nd step. (You might want to add column numbers and order columns.)
Or append \gexec in psql to execute the return value immediately. See:
How to force evaluation of subquery before joining / pushing down to foreign server
Be sure to defend against SQL injection:
INSERT with dynamic table name in trigger function
Define table and column names as arguments in a plpgsql function?
Asides
varchar(100) does not make much sense for identifiers, which are limited to 63 characters in standard Postgres:
Maximum characters in labels (table names, columns etc)
If you understand how the object identifier type regclass works, you might replace schema and table name with a singe regclass column.
I think you just need another query to get the list of columns you want.
Maybe something like (this is untested):
create or replace function public.get_table(_schema_name text, _table_name text, active boolean default true) returns setof record as $$
declare
entity_name text default schema_name || '.' || table_name;
r record;
columns varchar;
begin
-- Get the list of columns
SELECT string_agg(column_name, ', ')
INTO columns
FROM public.fields
WHERE fields.schema_name = _schema_name
AND fields.table_name = _table_name
AND fields.column_visible = TRUE;
-- Return rows from the specified table
RETURN QUERY EXECUTE 'select ' || columns || ' from ' || entity_name;
RETURN;
end
$$
language plpgsql;
Keep in mind that column/table references may need to be surrounded by double quotes if they have certain characters in them.
I implemented this function in my Postgres database: http://www.cureffi.org/2013/03/19/automatically-creating-pivot-table-column-names-in-postgresql/
Here's the function:
create or replace function xtab (tablename varchar, rowc varchar, colc varchar, cellc varchar, celldatatype varchar) returns varchar language plpgsql as $$
declare
dynsql1 varchar;
dynsql2 varchar;
columnlist varchar;
begin
-- 1. retrieve list of column names.
dynsql1 = 'select string_agg(distinct '||colc||'||'' '||celldatatype||''','','' order by '||colc||'||'' '||celldatatype||''') from '||tablename||';';
execute dynsql1 into columnlist;
-- 2. set up the crosstab query
dynsql2 = 'select * from crosstab (
''select '||rowc||','||colc||','||cellc||' from '||tablename||' group by 1,2 order by 1,2'',
''select distinct '||colc||' from '||tablename||' order by 1''
)
as ct (
'||rowc||' varchar,'||columnlist||'
);';
return dynsql2;
end
$$;
So now I can call the function:
select xtab('globalpayments','month','currency','(sum(total_fees)/sum(txn_amount)*100)::decimal(48,2)','text');
Which returns (because the return type of the function is varchar):
select * from crosstab (
'select month,currency,(sum(total_fees)/sum(txn_amount)*100)::decimal(48,2)
from globalpayments
group by 1,2
order by 1,2'
, 'select distinct currency
from globalpayments
order by 1'
) as ct ( month varchar,CAD text,EUR text,GBP text,USD text );
How can I get this function to not only generate the code for the dynamic crosstab, but also execute the result? I.e., the result when I manually copy/paste/execute is this. But I want it to execute without that extra step: the function shall assemble the dynamic query and execute it:
Edit 1
This function comes close, but I need it to return more than just the first column of the first record
Taken from: Are there any way to execute a query inside the string value (like eval) in PostgreSQL?
create or replace function eval( sql text ) returns text as $$
declare
as_txt text;
begin
if sql is null then return null ; end if ;
execute sql into as_txt ;
return as_txt ;
end;
$$ language plpgsql
usage: select * from eval($$select * from analytics limit 1$$)
However it just returns the first column of the first record :
eval
----
2015
when the actual result looks like this:
Year, Month, Date, TPV_USD
---- ----- ------ --------
2016, 3, 2016-03-31, 100000
What you ask for is impossible. SQL is a strictly typed language. PostgreSQL functions need to declare a return type (RETURNS ..) at the time of creation.
A limited way around this is with polymorphic functions. If you can provide the return type at the time of the function call. But that's not evident from your question.
Refactor a PL/pgSQL function to return the output of various SELECT queries
You can return a completely dynamic result with anonymous records. But then you are required to provide a column definition list with every call. And how do you know about the returned columns? Catch 22.
There are various workarounds, depending on what you need or can work with. Since all your data columns seem to share the same data type, I suggest to return an array: text[]. Or you could return a document type like hstore or json. Related:
Dynamic alternative to pivot with CASE and GROUP BY
Dynamically convert hstore keys into columns for an unknown set of keys
But it might be simpler to just use two calls: 1: Let Postgres build the query. 2: Execute and retrieve returned rows.
Selecting multiple max() values using a single SQL statement
I would not use the function from Eric Minikel as presented in your question at all. It is not safe against SQL injection by way of maliciously malformed identifiers. Use format() to build query strings unless you are running an outdated version older than Postgres 9.1.
A shorter and cleaner implementation could look like this:
CREATE OR REPLACE FUNCTION xtab(_tbl regclass, _row text, _cat text
, _expr text -- still vulnerable to SQL injection!
, _type regtype)
RETURNS text
LANGUAGE plpgsql AS
$func$
DECLARE
_cat_list text;
_col_list text;
BEGIN
-- generate categories for xtab param and col definition list
EXECUTE format(
$$SELECT string_agg(quote_literal(x.cat), '), (')
, string_agg(quote_ident (x.cat), %L)
FROM (SELECT DISTINCT %I AS cat FROM %s ORDER BY 1) x$$
, ' ' || _type || ', ', _cat, _tbl)
INTO _cat_list, _col_list;
-- generate query string
RETURN format(
'SELECT * FROM crosstab(
$q$SELECT %I, %I, %s
FROM %I
GROUP BY 1, 2 -- only works if the 3rd column is an aggregate expression
ORDER BY 1, 2$q$
, $c$VALUES (%5$s)$c$
) ct(%1$I text, %6$s %7$s)'
, _row, _cat, _expr -- expr must be an aggregate expression!
, _tbl, _cat_list, _col_list, _type);
END
$func$;
Same function call as your original version. The function crosstab() is provided by the additional module tablefunc which has to be installed. Basics:
PostgreSQL Crosstab Query
This handles column and table names safely. Note the use of object identifier types regclass and regtype. Also works for schema-qualified names.
Table name as a PostgreSQL function parameter
However, it is not completely safe while you pass a string to be executed as expression (_expr - cellc in your original query). This kind of input is inherently unsafe against SQL injection and should never be exposed to the general public.
SQL injection in Postgres functions vs prepared queries
Scans the table only once for both lists of categories and should be a bit faster.
Still can't return completely dynamic row types since that's strictly not possible.
Not quite impossible, you can still execute it (from a query execute the string and return SETOF RECORD.
Then you have to specify the return record format. The reason in this case is that the planner needs to know the return format before it can make certain decisions (materialization comes to mind).
So in this case you would EXECUTE the query, return the rows and return SETOF RECORD.
For example, we could do something like this with a wrapper function but the same logic could be folded into your function:
CREATE OR REPLACE FUNCTION crosstab_wrapper
(tablename varchar, rowc varchar, colc varchar,
cellc varchar, celldatatype varchar)
returns setof record language plpgsql as $$
DECLARE outrow record;
BEGIN
FOR outrow IN EXECUTE xtab($1, $2, $3, $4, $5)
LOOP
RETURN NEXT outrow
END LOOP;
END;
$$;
Then you supply the record structure on calling the function just like you do with crosstab.
Then when you all the query you would have to supply a record structure (as (col1 type, col2 type, etc) like you do with connectby.
I have created the following stored procedure, which basically receives a name of table, and a prefix. The function then finds all columns that share this prefix and returns as an output a 'select' query command ('myoneliner').
as follows:
CREATE OR REPLACE FUNCTION mytext (mytable text, myprefix text)
RETURNS text AS $myoneliner$
declare
myoneliner text;
BEGIN
SELECT 'SELECT ' || substr(cols,2,length(cols)-2) ||' FROM '||mytable
INTO myoneliner
FROM (
SELECT array(
SELECT DISTINCT quote_ident(column_name::text)
FROM information_schema.columns
WHERE table_name = mytable
AND column_name LIKE myprefix||'%'
order by quote_ident
)::text cols
) sub;
RETURN myoneliner;
END;
$myoneliner$ LANGUAGE plpgsql;
Call:
select mytext('dkj_p_k27ac','enri');
As a result of running this stored procedure and the 'select' that is following it, I get the following output at the Data Output window (all within one cell, named "mytext text"):
'SELECT enrich_d_dkj_p_k27ac,enrich_lr_dkj_p_k27ac,enrich_r_dkj_p_k27ac
FROM dkj_p_k27ac'
I would like to basically be able to take the output command line that I received as an output and execute it. In other words, I would like to be able and execute the output of my stored procedure.
How can I do so?
I tried the following:
CREATE OR REPLACE FUNCTION mytext (mytable text, myprefix text)
RETURNS SETOF RECORD AS $$
declare
smalltext text;
myoneliner text;
BEGIN
SELECT 'SELECT ' || substr(cols,2,length(cols)-2) ||' FROM '||mytable
INTO myoneliner
FROM (
SELECT array(
SELECT DISTINCT quote_ident(column_name::text)
FROM information_schema.columns
WHERE table_name = mytable
AND column_name LIKE myprefix||'%'
order by quote_ident
)::text cols
) sub;
smalltext=lower(myoneliner);
raise notice '%','my additional text '||smalltext;
RETURN QUERY EXECUTE smalltext;
END;
$$ LANGUAGE plpgsql;
Call function:
SELECT * from mytext('dkj_p_k27ac','enri');
But I'm getting the following error message, could you please advise what should I change in order for it to execute?:
ERROR: a column definition list is required for functions returning "record"
LINE 26: SELECT * from mytext('dkj_p_k27ac','enri');
********** Error **********
ERROR: a column definition list is required for functions returning "record"
SQL state: 42601
Character: 728
Your first problem was solved by using dynamic SQL with EXECUTE like Craig advised.
But the rabbit hole goes deeper:
CREATE OR REPLACE FUNCTION myresult(mytable text, myprefix text)
RETURNS SETOF RECORD AS
$func$
DECLARE
smalltext text;
myoneliner text;
BEGIN
SELECT INTO myoneliner
'SELECT '
|| string_agg(quote_ident(column_name::text), ',' ORDER BY column_name)
|| ' FROM ' || quote_ident(mytable)
FROM information_schema.columns
WHERE table_name = mytable
AND column_name LIKE myprefix||'%'
AND table_schema = 'public'; -- schema name; might be another param
smalltext := lower(myoneliner); -- nonsense
RAISE NOTICE 'My additional text: %', myoneliner;
RETURN QUERY EXECUTE myoneliner;
END
$func$ LANGUAGE plpgsql;
Major points
Don't cast the whole statement to lower case. Column names might be double-quoted with upper case letters, which are case-sensitive in this case (no pun intended).
You don't need DISTINCT in the query on information_schema.columns. Column names are unique per table.
You do need to specify the schema, though (or use another way to single out one schema), or you might be mixing column names from multiple tables of the same name in multiple schemas, resulting in nonsense.
You must sanitize all identifiers in dynamic code - including table names: quote_ident(mytable). Be aware that your text parameter to the function is case sensitive! The query on information_schema.columns requires that, too.
I untangled your whole construct to build the list of column names with string_agg() instead of the array constructor. Related answer:
Update multiple columns that start with a specific string
The assignment operator in plpgsql is :=.
Simplified syntax of RAISE NOTICE.
Core problem impossible to solve
All of this still doesn't solve your main problem: SQL demands a definition of the columns to be returned. You can circumvent this by returning anonymous records like you tried. But that's just postponing the inevitable. Now you have to provide a column definition list at call time, just like your error message tells you. But you just don't know which columns are going to be returned. Catch 22.
Your call would work like this:
SELECT *
FROM myresult('dkj_p_k27ac','enri') AS f (
enrich_d_dkj_p_k27ac text -- replace with actual column types
, enrich_lr_dkj_p_k27ac text
, enrich_r_dkj_p_k27ac text);
But you don't know number, names (optional) and data types of returned columns, not at creation time of the function and not even at call time. It's impossible to do exactly that in a single call. You need two separate queries to the database.
You could return all columns of any given table dynamically with a function using polymorphic types, because there is a well defined type for the whole table. Last chapter of this related answer:
Refactor a PL/pgSQL function to return the output of various SELECT queries
I have a situation where I want to return the join between two views. and that's a lot of columns. It was pretty easy in sql server. But in PostgreSQL when I do the join. I get the error "a column definition list is required".
Is there any way I can bypass this, I don't want to provide the definitions of returning columns.
CREATE OR REPLACE FUNCTION functionA(username character varying DEFAULT ''::character varying, databaseobject character varying DEFAULT ''::character varying)
RETURNS SETOF ???? AS
$BODY$
Declare
SqlString varchar(4000) = '';
BEGIN
IF(UserName = '*') THEN
Begin
SqlString := 'select * from view1 left join ' + databaseobject + ' as view2 on view1.id = view2.id';
End;
ELSE
Begin
SqlString := 'select * from view3 left join ' + databaseobject + ' as view2 on view3.id = view2.id';
End;
END IF;
execute (SqlString );
END;
$BODY$
Sanitize function
What you currently have can be simplified / sanitized to:
CREATE OR REPLACE FUNCTION func_a (username text = '', databaseobject text = '')
RETURNS ????
LANGUAGE plpgsql AS
$func$
BEGIN
RETURN QUERY EXECUTE
format ('SELECT * FROM %s v1 LEFT JOIN %I v2 USING (id)'
, CASE WHEN username = '*' THEN 'view1' ELSE 'view3' END
, databaseobject);
END
$func$;
You only need additional instances of BEGIN ... END in the function body to start separate code blocks with their own scope, which is rarely needed.
The standard SQL concatenation operator is ||. + is a "creative" addition of your former vendor.
Don't use CaMeL-case identifiers unless you double-quote them. Best don't use them at all See:
Are PostgreSQL column names case-sensitive?
varchar(4000) is also tailored to a specific limitation of SQL Server. It has no specific significance in Postgres. Only use varchar(4000) if you actually need a limit of 4000 characters. I would just use text - except that we don't need any variables at all here, after simplifying the function.
If you have not used format(), yet, consult the manual here.
Return type
Now, for your actual question: The return type for a dynamic query can be tricky since SQL requires that to be declared at call time at the latest. If you have a table or view or composite type in your database already matching the column definition list, you can just use that:
CREATE FUNCTION foo()
RETURNS SETOF my_view AS
...
Else, spell the column definition list with out with (simplest) RETURNS TABLE:
CREATE FUNCTION foo()
RETURNS TABLE (col1 int, col2 text, ...) AS
...
If you are making the row type up as you go, you can return anonymous records:
CREATE FUNCTION foo()
RETURNS SETOF record AS
...
But then you have to provide a column definition list with every call, so I hardly ever use that.
I wouldn't use SELECT * to begin with. Use a definitive list of columns to return and declare your return type accordingly:
CREATE OR REPLACE FUNCTION func_a(username text = '', databaseobject text = '')
RETURNS TABLE(col1 int, col2 text, col3 date)
LANGUAGE plpgsql AS
$func$
BEGIN
RETURN QUERY EXECUTE
format ($f$SELECT v1.col1, v1.col2, v2.col3
FROM %s v1 LEFT JOIN %I v2 USING (id)$f$
, CASE WHEN username = '*' THEN 'view1' ELSE 'view3' END
, databaseobject);
END
$func$;
For completely dynamic queries, consider building the query in your client to begin with, instead of using a function.
You need to understand basics first:
Refactor a PL/pgSQL function to return the output of various SELECT queries
PL/pgSQL in the Postgres manual
Then there are more advanced options with polymorphic types, which allow you to pass the return type at call time. More in the last chapter of:
Refactor a PL/pgSQL function to return the output of various SELECT queries