How Can I Efficiently Implement Parameterized ORDER BY and LIMIT Clauses in PostgreSQL Table Functions?

PostgreSQL Parameterized Order By / Limit in Table Function

Utilizing table functions in PostgreSQL enables efficient data manipulation and retrieval. However, when dealing with large datasets, it becomes crucial to apply sorting and pagination to handle results effectively.

Consider the following scenario: we have a table function, getStuff, that performs a simple SELECT query on a table named stuff:

CREATE OR REPLACE FUNCTION getStuff(param character varying)
  RETURNS SETOF stuff AS
$BODY$
    select *
    from stuff
    where col = 
$BODY$
  LANGUAGE sql;

Initially, we invoke the function as follows:

select * from getStuff('hello');

However, to optimize performance, we need to apply an ORDER BY clause and a LIMIT clause. Unfortunately, executing a query like this:

select * from getStuff('hello') order by col2 limit 100;

will retrieve all rows from the stuff table and then order and limit them, resulting in inefficient processing.

Furthermore, PostgreSQL does not provide an inherent method to pass ORDER BY arguments to an SQL language function, as only values can be transferred. Constructing the query within a plpgsql function and executing it via EXECUTE is an alternative approach, but it's not the most elegant solution.

The Solution:

Fortunately, a plpgsql function offers an effective solution for this scenario. We can modify the getStuff function to accept additional parameters for ORDER BY and LIMIT:

CREATE OR REPLACE FUNCTION getStuff(param character varying, orderby character varying, _limit int)
  RETURNS SETOF stuff AS
$func$
BEGIN
   RETURN QUERY EXECUTE '
      SELECT *
      FROM   stuff
      WHERE  col = 
      ORDER  BY ' || quote_ident(_orderby) || ' ASC
      LIMIT  '
   USING _param, _limit;
END
$func$  LANGUAGE plpgsql;

Now, we can invoke the function with the desired parameters:

SELECT * FROM getStuff('hello', 'col2', 100);

The RETURN QUERY EXECUTE statement efficiently retrieves the results of the query within the function.

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