sql - Postgres : correlated subquery with NOT EXISTS

Question

在 Oracle SQL 中，您可以轻松地根据相关子查询中的 NOT EXISTS 条件进行更新。这对于根据另一个查询或 ID 列表进行更新很有用。

子查询机制在 Postgres 中是不同的...我怎样才能达到相同的目标？ http://sqlfiddle.com/#!1/1dbb8/55

在 Oracle 上你会怎么做

UPDATE UserInfo a
SET a.username = 'not found'
WHERE NOT EXISTS (SELECT 'X' 
              FROM UserOrder b
              WHERE b.userid = a.userid)
AND a.userid in (1,2,3);

Postgres NOT EXISTS 查询:有效

SELECT u.userid, u.username
FROM UserInfo AS u
WHERE NOT EXISTS
  ( SELECT *
    FROM UserOrder AS o
    WHERE o.userid = u.userid
);

Postgres NOT EXISTS 更新:不起作用

UPDATE UserInfo
SET username = 'not found'
FROM (SELECT u.userid
    FROM UserInfo AS u
    WHERE NOT EXISTS
       ( SELECT *
         FROM UserOrder AS o
         WHERE o.userid = u.userid
       )) em
WHERE em.userid = UserInfo.userid;

Answer 1

显然，每次您“运行脚本”时，Sqlfiddle 都会重新生成数据库内容。在与更新相同的脚本中运行选择。

您从 sqlfiddle 进行的 Oracle 查询几乎可以正常工作，但您忘记为 userid 参数设置别名。正确查询:

/* How you would do it on Oracle */
UPDATE UserInfo
SET username = 'not found'
WHERE NOT EXISTS (SELECT 'X' 
                  FROM UserOrder b
                  WHERE b.userid = userinfo.userid);