程序：

CREATE OR REPLACE FUNCTION kappend(anynonarray, anyelement) RETURNS text AS$$SELECT $1 || $2;$$ LANGUAGE SQL;

调用方法(错误):

pgsql=# select kappend('def','abc');ERROR:  could not determine polymorphic type because input has type "unknown"pgsql=#

调用方法(正确):

pgsql=# select kappend('def'::text,'abc'::text); kappend --------- defabc(1 row)pgsql=#