Declare a Table as a variable in a stored procedure? - postgresql

Question

I am currently working a stored procedure capable of detecting continuity on a specific set of entries..
The specific set of entries is extracted from a sql query
The function takes in two input parameter, first being the table that should be investigated, and the other being the list of ids which should be evaluated.
For every Id I need to investigate every row provided by the select statement.
DROP FUNCTION IF EXISTS GapAndOverlapDetection(table_name text, entity_ids bigint[]);
create or replace function GapAndOverlapDetection ( table_name text, enteity_ids bigint[] )
returns table ( entity_id bigint, valid tsrange, causes_overlap boolean, causes_gap boolean)
as $$
declare
x bigint;
var_r record;
begin
FOREACH x in array $2
loop
EXECUTE format('select entity_id, valid from' ||table_name|| '
where entity_id = '||x||'
and registration #> now()::timestamp
order by valid ASC') INTO result;
for var_r in result
loop
end loop;
end loop ;
end
$$ language plpgsql;
select * from GapAndOverlapDetection('temp_country_registration', '{1,2,3,4}')
I currently get an error in the for statement saying
ERROR: syntax error at or near "$1"
LINE 12: for var_r in select entity_id, valid from $1

Answer 1

You can iterate over the result of the dynamic query directly:
create or replace function gapandoverlapdetection ( table_name text, entity_ids bigint[])
returns table (entity_id bigint, valid tsrange, causes_overlap boolean, causes_gap boolean)
as $$
declare
var_r record;
begin
for var_r in EXECUTE format('select entity_id, valid
from %I
where entity_id = any($1)
and registration > now()::timestamp
order by valid ASC', table_name)
using entity_ids
loop
... do something with var_r
-- return a row for the result
-- this does not end the function
-- it just appends this row to the result
return query
select entity_id, true, false;
end loop;
end
$$ language plpgsql;
The %I injects an identifier into a string and the $1 inside the dynamic SQL is then populated through passing the argument with the using keyword

Answer 2

Firstly, decide whether you want to pass the table's name or oid. If you want to identify the table by name, then the parameter should be of text type and not regclass.
Secondly, if you want the table name to change between executions then you need to execute the SQL statement dynamically with the EXECUTE statement.