用可能为空值更新非空字段

Question

在下面的查询中：

update collect_irc_deploy c
set hid = (select id
           from auth_hierarchy
           where fqdn = (select location
                         from reserve
                         where id=c.rid
                        )
          )
where hid = 0 and rid is not null

子查询 select id from auth_hierarchy where fqdn = (select location from Reserve where id = c.rid) 可能返回 NULL 而字段 hid 是NOT NULL。

如何修改语句，以便在子查询返回 NULL 时跳过该数据项，而不是使整个执行失败？

Answer 1

您可以使用 update...join 语法来确保仅更新连接的行：

update collect_irc_deploy
join reserve on reserve.id = collect_irc_deploy.rid
join auth_hierarchy on auth_hierarchy.fqdn = reserve.location
set collect_irc_deploy.hid = auth_hierarchy.id
where collect_irc_deploy.hid = 0 and collect_irc_deploy.rid is not null

Answer 2

使用 UPDATE IGNORE 解决了我的问题。但它会生成警告消息。