postgresql function

PostgreSQL如何满足已经存在则更新, 不存在则插入的需求.
A :
digoal=> create table exists_test (id int primary key,info text);NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "exists_test_pkey" for table "exists_test"CREATE TABLEdigoal=> create or replace function insert_exists_test(i_id int,i_info text) returns void as $BODY$declarebeginperform 1 from exists_test where id=i_id;if not found theninsert into exists_test(id,info) values (i_id,i_info);return;elseupdate exists_test set info=i_info where id=i_id;return;end if;exceptionwhen others thenraise exception 'Insert exists_test(id,info) values(%,%) error.',i_id,i_info;return;end;$BODY$ language plpgsql;digoal=> select insert_exists_test(1,'digoal');digoal=> select insert_exists_test(1,'adigoal');digoal=> select * from exists_test ; id |  info   ----+---------  1 | adigoal