CREATE OR REPLACE  FUNCTION find_in_set(str text, strlist text) RETURNS int
AS
DECLARE b1 VARCHAR;
begin
 b1:=array_position(string_to_array($2, ','),$1); 
 RETURN b1;
end;

SELECT t.dept_id FROM sys_dept t WHERE find_in_set(#{deptId}, ancestors) 

SELECT t.dept_id FROM sys_dept t WHERE find_in_set(#{deptId}, ancestors)
SELECT t.dept_id FROM sys_dept t WHERE position(#{deptId} in ancestors)