Convert string to column name - postgresql

I'm trying to write a simple postgres function which looks more or less like that:
CREATE OR REPLACE FUNCTION USER_TOTALS(column_name varchar, in_t users) RETURNS float AS $$
DECLARE
sum float;
BEGIN
sum = (SELECT SUM($1) FROM jobs WHERE jobs.technician_id = in_t.id);
RETURN sum;
END;
$$ LANGUAGE plpgsql;
And i need to use it like that:
SELECT users.*, USER_TOTALS('jobs.price', users.*) AS total_price_value FROM users;
Hovewer, that's obviously not working cause SUM() function expects to get a column name but my code passes a varchar to it, so the error says:
Function sum(character varying) does not exist
The question is - can i somehow cast a varchar variable to column name var type? I've been googling for this thing for about 2 hours now and i have no idea how can i make that happen.


A recommended form:
CREATE OR REPLACE FUNCTION USER_TOTALS(column_name varchar, in_t users)
RETURNS float AS $$
DECLARE
sum float;
BEGIN
EXECUTE format('SELECT SUM(%I) FROM jobs WHERE jobs.technician_id=$1', column_name)
INTO sum
USING in_t;
RETURN sum;
END;
$$ LANGUAGE plpgsql;


CREATE OR REPLACE FUNCTION USER_TOTALS(column_name varchar, in_t users) RETURNS float AS $$
DECLARE
sum float;
BEGIN
EXECUTE 'SELECT SUM('||column_name||') FROM jobs WHERE jobs.technician_id='||in_t INTO sum;
RETURN sum;
END;
$$ LANGUAGE plpgsql;

Related

Create a stored procedure to Delete Records postgres

I have created a function to delete multiple records.In our table contain id as type uuid.
We get the input is like array of ids.
CREATE OR REPLACE FUNCTION public.deletetVersion(item_list uuid[])
RETURNS TABLE(id uuid[])
LANGUAGE 'plpgsql'
COST 100
VOLATILE PARALLEL UNSAFE
ROWS 1000
AS $BODY$
BEGIN
RETURN QUERY
DELETE FROM version WHERE id = ANY(item_list);
END;
$BODY$;
SELECT * from deletetVersion(Array['b6ad1912-e4f1-4419-831a-c70df89ffd63','877898f0-2f3f-4890-a658-898e35ffee3a'])
But i got an error like:
Anyone please help me
ERROR: function deletetversion(text[]) does not exist

it is because the
Array['b6ad1912-e4f1-4419-831a-c70df89ffd63','877898f0-2f3f-4890-a658-898e35ffee3a']
is treated as text[]
try the following
Array['b6ad1912-e4f1-4419-831a-c70df89ffd63'::uuid,'877898f0-2f3f-4890-a658-898e35ffee3a'::uuid]
as a parameter to your function
for example
CREATE OR REPLACE FUNCTION public.test_uuid(item_list uuid[])
RETURNS TABLE(id uuid[])
LANGUAGE 'plpgsql'
COST 100
VOLATILE PARALLEL UNSAFE
ROWS 1000
AS $BODY$
BEGIN
RETURN QUERY
SELECT item_list;
END;
$BODY$;
SELECT * from test_uuid(Array['b6ad1912-e4f1-4419-831a-c70df89ffd63'::uuid])
In case of deletion
CREATE OR REPLACE FUNCTION public.test_uuid(item_list uuid[])
RETURNS VOID
LANGUAGE 'plpgsql'
COST 100
VOLATILE PARALLEL UNSAFE
ROWS 1000
AS $BODY$
BEGIN
RETURN QUERY
DELETE from tableName WHERE id = ANY(item_list);
END;
$BODY$;

Your function should return either setof uuid - i.e. a table of uuid-s - or uuid[]. I would prefer the first. You do not need PL/pgSQL, plain SQL is enough. So the function is:
create or replace function public.deletetVersion(item_list uuid[])
returns setof uuid language 'sql' as
$$
delete from version where id = any(item_list) returning id;
$$;
The version returning an array is a bit more complex:
create or replace function public.deletetVersion(item_list uuid[])
returns uuid[] language 'sql' as
$$
with t(d_id) as
(
delete from version where id = any(item_list) returning id
)
select array_agg(d_id) from t;
$$;
And - as #Ibrahimshamma says - you may need to cast the argument to uuid[].

How to combine custiom defined variables and display them as records of a table in postgres

I'm a beginner in plpgsql and working on a project which requires me to write a function that returns two variables in the form of 2 columns (res,Result). I've done a quite a bit of searching but didn't find answer for the same. The reference to my code is below
CREATE OR REPLACE FUNCTION propID(character varying)
RETURNS SETOF RECORD AS $val$
DECLARE
t_row record;
res BOOLEAN;
result character varying;
value record;
BEGIN
FOR t_row IN SELECT property_id FROM property_table WHERE ward_id::TEXT = $1 LOOP
RAISE NOTICE 'Analyzing %', t_row;
res := false; -- here i'm going to replace this value with a function whos return type is boolean in future
result := t_row.property_id;
return next result; --here i want to return 2 variables (res,result) in the form of two columns (id,value)
END LOOP;
END;
$val$
language plpgsql;
Any help on the above query would be very much appreciated.

Assuming that property_id and ward_id are integers you can achieve your goal in a simple query like this:
select some_function_returning_boolean(property_id), property_id
from property_table
where ward_id = 1; -- input parameter
If you absolutely need a function, it can be an SQL function like
create or replace function prop_id(integer)
returns table (res boolean, id int) language sql
as $$
select some_function_returning_boolean(property_id), property_id
from property_table
where ward_id = $1
$$;
In a plpgsql function you should use return query:
create or replace function prop_id(integer)
returns table (res boolean, id int) language plpgsql
as $$
begin
return query
select some_function_returning_boolean(property_id), property_id
from property_table
where ward_id = $1;
end
$$;

Porting strategy pattern from SQL Server to Postgresql

SQL Server has a feature whereby you can call a function or stored procedure with a variable name for the func/proc name. Toy example:
declare #name sysname;
declare #method int = 1;
set #name = IIF(#method = 1, N'Newton', N'Taylor')
declare #sqrt float;
exec #sqrt = #name 42
This will call either Newton or Taylor depending on the value of #method. Using this, it is possible to implement the strategy or command OOP patterns in T-SQL. Where I work, we use it for just that purpose.
Now that I'm learning Postgresql, I'm wondering how I would do something similar in pgplsql. Any tips appreciated!

If all called functions return a single value of the same data type and take a single parameter of the same data type, you can do that with dynamic SQL in Postgres as well:
create or replace function evaluate(p_input integer, p_method text)
returns float
as
$$
declare
l_result float;
begin
execute 'select '||p_method||'($1)'
using p_input
into l_result;
return l_result;
end;
$$
language plpgsql;
select evaluate(42, 'sqrt'); returns 6.48074069840786
select evaluate(1, 'exp'); returns 2.718281828459045
This works with multiple parameters as well:
create or replace function evaluate(p_arg_1 integer, p_arg_2 text, p_method text)
returns float
as
$$
declare
l_result float;
begin
execute 'select '||p_method||'($1, $2)'
using p_arg_1, p_arg_2
into l_result;
return l_result;
end;
$$
language plpgsql;

Passing the table as a parameter

I have to convert from lat and long to geom to use PostGIS. My problem, I have various tables from different locations and I want to pass the table as a parameter to the function. I'm trying this:
CREATE or REPLACE FUNCTION convert_from_lon_lat(float,float,character varying)
RETURNS integer AS $$
select id from $3 as vertices
order by vertices.geom <-> ST_SetSrid(ST_MakePoint($1,$2),4326) LIMIT 1;
$$ LANGUAGE SQL;
but I get a syntax error.
EDIT1:
So I changed the previous code to this:
CREATE or REPLACE FUNCTION convert_from_lon_lat(long float, lat float, _table character varying) RETURNS integer AS $$
BEGIN
EXECUTE('select id from _table as vertices order by vertices.geom <-> ST_SetSrid(ST_MakePoint(long,lat),4326) LIMIT 1;');
END;
$$ LANGUAGE plpgsql;
it creates without any problem, but when I call it `convert_from_lon_lat(long1, long2, my_table)
I get and error:
ERROR: relation "_table" does not exist
It's not passing the table name as an argument
EDIT 2:
CREATE or REPLACE FUNCTION convert_from_lon_lat(long float, lat float, tbl character varying) RETURNS integer AS $func$
BEGIN
EXECUTE format('select id from %s order by %s.the_geom <-> ST_SetSrid(ST_MakePoint('|| long || ','|| lat ||'),4326) LIMIT 1;', tbl, tbl);
END;
$func$ LANGUAGE plpgsql;
Now when I call the function, I get an `ERROR: control reached end of function without RETURN``
I tried RETURN QUERY EXECUTE format('... but I get a ERROR: cannot use RETURN QUERY in a non-SETOF function

AS #dezso mentioned, you'll need dynamic SQL in this case.
Dynamic SQL with EXECUTE
So, you're on the right track; forming a dynamic SQL statement using PL/pgSQL, but you just need the finishing touches:
CREATE or REPLACE FUNCTION convert_from_lon_lat(long float, lat float, _table text)
RETURNS integer AS $$
BEGIN
RETURN QUERY EXECUTE format('SELECT id FROM %I AS vertices
ORDER BY vertices.geom <->ST_SetSrid(ST_MakePoint(long,lat),4326) LIMIT 1;',_table);
END
$$ LANGUAGE plpgsql;
I believe this should solve your issues.
Note: We've discovered an error with the above solution and using SETOF, I've attempted to correct the issues below.
EDIT:
A few edits here, hopefully one solution will fix your issue. Also, please excuse any syntax errors in my previous & current solutions; I don't have time to test them right now. :(
1) You could just try returning a SETOF integers, knowing that of course you'll only return the one. Your return type in this case will then be a single, one-column row containing an integer.
CREATE or REPLACE FUNCTION convert_from_lon_lat(long float, lat float, _table text)
RETURNS SETOF integer AS $$
BEGIN
RETURN QUERY EXECUTE format('SELECT id FROM %I AS vertices
ORDER BY vertices.geom <->ST_SetSrid(ST_MakePoint(long,lat),4326) LIMIT 1;',_table);
END
$$ LANGUAGE plpgsql;
and then call as:
SELECT * FROM convert_from_lon_lat(...);
2) To specifically return an integer, I think you can try this:
CREATE or REPLACE FUNCTION convert_from_lon_lat(long float, lat float, _table text)
RETURNS integer AS $$
DECLARE
return_id integer;
BEGIN
EXECUTE format('SELECT id FROM %I AS vertices
ORDER BY vertices.geom <->ST_SetSrid(ST_MakePoint(long,lat),4326) LIMIT 1;',_table)
INTO return_id;
RETURN return_id;
END
$$ LANGUAGE plpgsql;

Rename the column name of a stored function

I've got a postgresql stored procedure, which is returning an integer.
When I call that function, the result is returned with the function name as column name.
For example the name of the function is: "add-person". The column name, when invoking the function, is "add-person".
Is there a way to make the database return the integer with a self-choosen column name? For example "id"?
I think it is pretty easy, but I currently miss the forests for the trees..
Edit:
What i'd missed to tell, is that the return value is a variable, like so:
CREATE OR REPLACE FUNCTION "scheme"."add-person"(arggivenname character varying, argfamilyname character varying) RETURNS integer AS
$BODY$
DECLARE
varResponse integer;
BEGIN
-- Operations before
INSERT INTO "scheme"."table"
(
given_name,
family_name
)
VALUES
(
arggivenname,
argfamilyname
)
RETURNING
"id"
INTO
varResponse;
-- Operations after
RETURN varResponse;
END;
$BODY$
LANGUAGE plpgsql VOLATILE COST 100;

You can us the AS statement for that. That means:
Select add-person() AS yourcolumnname

To have a named column from a function it is necessary to create a type and return that type from the function
create type mytype as (mycolumn integer);
create or replace function ri()
returns mytype as $$
select 1;
$$ language sql;
select * from ri();
mycolumn
----------
1
Edit
Or much simpler without the type creation as in #pozs comment:
create or replace function ri(out mycolumn integer)
as $$
select 1;
$$ language sql;