检测到PostgreSQL SQL函数中的UPDATE失败(不是PL/pgSQL)

Question

为了模仿MySQL-REPLACE语句(又名UPSERT),我需要尝试更新记录,如果失败 - 请插入它.但是如何在SQL过程中检测到UPDATE失败？

begin transaction;

create table pref_users (
       id varchar(32) primary key,
       first_name varchar(32),
       last_name varchar(32),
       female boolean,
       avatar varchar(128),
       city varchar(32),
       lat real check (-90 <= lat and lat <= 90),
       lng real check (-90 <= lng and lng <= 90),
       last_login timestamp default current_timestamp,
       last_ip inet,
       medals smallint check (medals > 0)
);
create table pref_rate (
       obj varchar(32) references pref_users(id),
       subj varchar(32) references pref_users(id),
       good boolean,
       fair boolean,
       nice boolean,
       about varchar(256),
       last_rated timestamp default current_timestamp
);

create table pref_money (
       id varchar(32) references pref_users,
       yw char(7) default to_char(current_timestamp, 'YYYY-WW'),
       money real
);
create index pref_money_yw_index on pref_money(yw);

create or replace function update_pref_users(id varchar,
       first_name varchar, last_name varchar, female boolean,
       avatar varchar, city varchar, last_ip inet) returns void as $$

       update pref_users set
            first_name = $2,
            last_name = $3,
            female = $4,
            avatar = $5,
            city = $6,
            last_ip = $7
        where id = $1;

        -- XXX how to detect failure here? XXX

       insert into pref_users(id, first_name, last_name,
            female, avatar, city, last_ip)
            values ($1, $2, $3, $4, $5, $6, $7);
$$ language sql;

commit;

我的update_pref_users SQL函数中是否需要第二对BEGIN/COMMIT？

Answer 1

你不能使用SQL作为一种语言,你需要pl/pgsql,因为SQL中缺少if-else结构.

在pl/pgsql中,您可以使用特殊变量FOUND来查看查询是否找到了某些内容.

UPDATE ...;
IF NOT FOUND THEN -- UPDATE didn't touch anything
  INSERT ...;
END IF;

不需要额外的SELECT语句.