checking existence of a table before updating its SERIAL

Hello,

We're updating the SERIAL of a bunch of tables with a SQL script which
does for any table:

/* table: idm_tasktab */
DO $$
DECLARE
  max_id int;
BEGIN
  SELECT INTO max_id GREATEST(COALESCE(max(taskid), 0),0) + 1 FROM idm_tasktab;
  RAISE NOTICE '% % %', 'idm_tasktab', 'taskid', max_id ;
  EXECUTE 'ALTER SEQUENCE idm_tasktab_taskid_seq RESTART ' || max_id::text;
END $$ LANGUAGE plpgsql;

Can some kind soul help me with doing a test for the existence of the
table to avoid the error message about non existing relation? 

Thanks in advance.

    matthias

-- 
Matthias Apitz, ✉ guru@unixarea.de, http://www.unixarea.de/ +49-176-38902045
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