where子句postgresql中的函数（动态列）

Question

I created func_leonard_test2 function which returns teach_fra=true when

SELECT func_leonard_test2('Français-Philosophie');

func_leonard_test2

CREATE OR REPLACE FUNCTION public.func_leonard_test2(
    IN url text,
    OUT translation text)
  RETURNS text AS
$BODY$BEGIN

SELECT CONCAT(translate,'=true') INTO translation FROM seo_content WHERE name=url;     

END;$BODY$

I want to add the function in a where clause like below

SELECT description FROM c_users WHERE (SELECT func_leonard_test('Français-Philosophie')) LIMIT 10;

but i get the error ERROR: argument of WHERE must be type boolean, not type text

How can i make the function work in the WHERE clause ?

Thank you for your time.

Answer 1

Your function returns a string. You need some sort of string comparison. Someting like:

WHERE func_leonard_test('Français-Philosophie') IS NOT NULL

or

WHERE func_leonard_test('Français-Philosophie') = 'ABC'

Also, the SELECT is not necessary.

EDIT:

I think you want the function to return a boolean. One way to write it would be:

CREATE OR REPLACE FUNCTION public.func_leonard_test2 (
    IN in_url text
   )
  RETURNS boolean AS
$BODY$BEGIN
    RETURN (SELECT (c.translate = true)
            FROM seo_content c
            WHERE c.name = in_url
           );     
END;$BODY$

Then you can use:

WHERE func_leonard_test('Français-Philosophie')