SQL 来自左连接的 Postgres 更新

Postgres update from left join

提问by alfoks

I'm new in PostgreSQL and trying to convert a query from SQL Server.

我是 PostgreSQL 新手，正在尝试从 SQL Server 转换查询。

I have a table Users with, among others, the columns bUsrActive, bUsrAdmin and sUsrClientCode. I want to update Users and set bUsrActive = false if there does not exist a another user with the same sUsrClientCode where bUsrAdmin = true and bUsrActive = true.

我有一个表用户，其中包括 bUsrActive、bUsrAdmin 和 sUsrClientCode 列。如果不存在具有相同 sUsrClientCode 的另一个用户，其中 bUsrAdmin = true 和 bUsrActive = true，我想更新用户并设置 bUsrActive = false。

In SQL Server I have this query

在 SQL Server 我有这个查询

UPDATE u SET u.bUsrActive = 0
FROM Users u
LEFT JOIN Users u2 ON u.sUsrClientCode = u2.sUsrClientCode AND u2.bUsrAdmin = 1 AND u2.bUsrActive = 1
WHERE u.bUsrAdmin = 0 AND u.bUsrActive = 1 AND u2.nkUsr IS NULL

I'm trying to convert this to postgres. I wrote 3 approaches.

我正在尝试将其转换为 postgres。我写了3种方法。

1) My first attempt. Obviously not working.

1）我的第一次尝试。显然不工作。

UPDATE Users u
    SET bUsrActive = false
FROM Users u2
WHERE u.sUsrClientCode = u2.sUsrClientCode AND u2.bUsrAdmin = true AND u2.bUsrActive = true
AND u.bUsrAdmin = false AND u.bUsrActive = true AND u2.nkUsr IS NULL;

2) I understand why it's not working (it updates all users). I just can't figure out how can I reference table Users u in the UPDATE ... SET part.

2）我明白为什么它不起作用（它更新所有用户）。我只是不知道如何在 UPDATE ... SET 部分引用表 Users u 。

UPDATE Users
    SET bUsrActive = false
FROM Users u
LEFT JOIN Users u2 ON u.sUsrClientCode = u2.sUsrClientCode AND u2.bUsrAdmin = true AND u2.bUsrActive = true
WHERE u.bUsrAdmin = false AND u.bUsrActive = true AND u2.nkUsr IS NULL;

3) The following is working, but not using join.

3）以下有效，但不使用join。

UPDATE Users
    SET bUsrActive = false
WHERE  NOT EXISTS (
    SELECT 1
    FROM Users u
    WHERE u.sUsrClientCode = Users.sUsrClientCode AND u.bUsrAdmin = true AND u.bUsrActive = true
) AND Users.bUsrAdmin = false AND Users.bUsrActive = true;

I'll probably go with the last solution. I just wanted to know if it's possible to do what I want using a left join.

我可能会采用最后一个解决方案。我只是想知道是否可以使用左连接来做我想做的事情。

回答by Daniel Vérité

Here's a generic way to transform this update query from SQL-server form to PostgreSQL:

这是将此更新查询从 SQL 服务器形式转换为 PostgreSQL 的通用方法：

UPDATE Users
 SET bUsrActive = false
WHERE
 ctid IN (
   SELECT u.ctid FROM Users u
      LEFT JOIN Users u2 ON u.sUsrClientCode = u2.sUsrClientCode AND u2.bUsrAdmin = 1 AND u2.bUsrActive = 1
    WHERE u.bUsrAdmin = 0 AND u.bUsrActive = 1 AND u2.nkUsr IS NULL
)

ctidis a pseudo-column that points to the unique location of a row. You could use instead the primary key of the table if it had one.

ctid是一个伪列，指向行的唯一位置。如果有主键，您可以改用表的主键。

The query #2 from the question doesn't do what you expect because the updated table Usersis never joined to the same table Users uin the FROM clause. Just as when you put a table name twice in a FROM clause, they don't get implicitly joined or bound together, they are considered as two independant sets of rows.

问题中的查询 #2 不符合您的预期，因为更新后的表Users从未连接到Users uFROM 子句中的同一个表。就像在 FROM 子句中两次放入表名一样，它们不会隐式连接或绑定在一起，它们被视为两个独立的行集。

回答by Clive Paterson

I think this is the correct way of doing 2) I belive it's more optimal/efficient than doing a sub select.

我认为这是正确的做法 2) 我相信它比做子选择更优化/更有效。

UPDATE Users uOrig
    SET bUsrActive = false
FROM Users u
      LEFT JOIN Users u2 ON u.sUsrClientCode = u2.sUsrClientCode AND u2.bUsrAdmin = 1 AND u2.bUsrActive = 1
WHERE u.bUsrAdmin = 0 AND u.bUsrActive = 1 AND u2.nkUsr IS NULL
    and uOrig.sUsrClientCode = u.sUsrClientCode;