(PostgreSQL) How to create a function based on a text argument and return a list

Question

I have a SELECT statement that returns a list:

SELECT  "db"."accounts"."account" as account
FROM db.accounts
WHERE db.accounts.level = 'Level 4' AND db.accounts.report = 'Report A'

As report can be either Report A or Report B, I want to create a function that the user chooses which report, something like: get_account('Report A').

What I've tried:

CREATE TYPE get_accounts_results AS ARRAY[];

CREATE OR REPLACE FUNCTION get_accounts(report TEXT) RETURNS get_accounts_results AS

    $$ 
        SELECT  "db"."accounts"."account" as account
        FROM db.accounts
        WHERE db.accounts.level = 'Level 4' AND db.accounts.report = $1
    $$

    LANGUAGE SQL;

SELECT get_accounts('Report A') AS report_account;

This gives me back 1 value only, when in fact I need n values - the quantity of values on this list is dynamic. Probably the type being created is wrong, but I didn't find anything that made sense in this scenario.

My question is: how to adjust this query in order to get the result of the created function on a list?

(PS: My end objective is to be able to iterate through this list to make a query that dynamically adds the query result to a materialized view)

Answer 1

You need to define your function to return a table. And you don't really need the type definition either:

CREATE OR REPLACE FUNCTION get_accounts(p_report TEXT) 
  RETURNS table(report_account text)
AS
$$ 
  SELECT act.account
  FROM db.accounts as act
  WHERE act.level = 'Level 4' 
    AND act.report = p_report;
$$
LANGUAGE SQL;

The above assumes that the column account is of type text . If it is not, then you need to adjust the data type in RETURNS table(report_account text) accordingly.

Then you can call it like this:

SELECT *
FROM get_accounts('Report A');

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Unrelated, but: a column alias that is the same as the column name doesn't really make sense. "account" as account" is exactly the same thing as "account"