Postgres 给出关系不存在别名错误

Question

WITH TAB AS 
(
 SELECT id,flag FROM source where flag IS NULL and Data= '151234567890' ORDER BY 1 OFFSET 
 (
  SELECT COUNT(*) FROM source where flag IS NULL and Data = '151234567890' ) - 96 FETCH FIRST 96 ROWS ONLY )
 UPDATE TAB SET flag = 'Z';

以上查询在 MS Sql 中运行良好，但在 postgres

中运行时显示此错误

ERROR:  relation "tab" does not exist
LINE 9:  UPDATE TAB SET flag = 'Z';

Answer 1

在 MS Sql 服务器中可以更新 CTE。

在 Postgresql 中，您可以 link 到 CTE 进行更新。

例如：

WITH CTE AS (
  SELECT id FROM source
  WHERE Data= '151234567890' 
   AND flag IS NULL
  ORDER BY id DESC
  FETCH FIRST 96 ROWS ONLY
) 
UPDATE source t
SET flag = 'Z'
FROM CTE c
WHERE t.id = c.id;

但是，此类更新假定 table 中的 ID 是唯一的。

但是，要标记最新的重复项，可以对其进行简化。

UPDATE source tgt
SET flag = 'Z'
FROM source src
WHERE src.Data = '151234567890'
  AND tgt.Data = src.Data
  AND tgt.id = src.id
  AND tgt.ctid > src.ctid
  AND tgt.flag IS NULL;

或者如果您想标记更高的金额。
使用 ROW_NUMBER 可能会有帮助。

WITH CTE AS (
  SELECT ctid, id, Data, Amt
  , ROW_NUMBER() OVER (PARTITION BY Data, id ORDER BY Amt) AS rn
  FROM source
  WHERE Data= '151234567890' 
   AND flag IS NULL
) 
UPDATE source t
SET flag = 'Z'
FROM CTE c
WHERE c.rn > 1
  AND t.id = c.id
  AND t.Data = c.Data
  AND t.ctid = c.ctid;

测试 db<>fiddle here

Postgres 给出关系不存在别名错误

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