在添加唯一约束的列中删除重复的值

Question

我有一个带有displayName列的表，我添加了一个“唯一”约束。我试图编写一个迁移，将任何非唯一的displayName设置为null，只保留具有较低用户ID的displayName。这里是我的查询：

UPDATE "User" SET "displayName" = NULL 
      WHERE id IN (SELECT id, 
         FROM (SELECT id, 
            ROW_NUMBER() OVER (partition BY "displayName" ORDER BY id) AS rnum 
           FROM "User") t 
         WHERE t.rnum > 1); 

当我试图运行迁移我回来了“错误：语法错误在或接近”FROM“”。

感谢

Answer 1

为什么不直接写为：

UPDATE "User" 
    SET "displayName" = NULL 
    WHERE id > (SELECT MIN(u2.id) 
       FROM "User" u2 
       WHERE u2."displayName" = u."displayName" 
       ); 

无论数据库使用的是，这也应该是能够在"User"("displayName", id)采取指数的优势。

Answer 2

更简单的方法是使用CTE或子查询，像这样....

WITH X AS 
(
SELECT id 
    , [displayName] 
    , ROW_NUMBER() OVER (partition BY [displayName] ORDER BY id) AS rnum 
FROM [User] 
) 
UPDATE X 
SET [displayName] = NULL 
WHERE rnum > 1 

OR

UPDATE X 
SET [displayName] = NULL 
FROM (
     SELECT id 
      , [displayName] 
      , ROW_NUMBER() OVER (partition BY [displayName] ORDER BY id) AS rnum 
     FROM [User] 
    ) x 
WHERE rnum > 1 

而且在一个侧面说明，在唯一约束显示名称真的：S ....