PostgreSQL 中的问题（错误：关系“a”不存在）

Question

SQL 查询 (PostgreSQL) 如下所示：

UPDATE a
SET "PropertyAddress" = COALESCE(a."PropertyAddress", b."PropertyAddress")
FROM "NashvilleHousingData" a
INNER JOIN "NashvilleHousingData" b
    ON a."ParcelID" = b."ParcelID"
    AND a."UniqueID" <> b."UniqueID"
WHERE a."PropertyAddress" IS NULL;

错误是relation "a" does not exist

我尝试了关于代码公共或方案中的概念的其他建议，但它仍然不起作用。请帮忙

Answer 1

这不是 Postgres 处理多个表的更新的方式。您不要在from 子句中重复该表：

UPDATE "NashvilleHousingData" nhd
    SET "PropertyAddress" = COALESCE(nhd."PropertyAddress", nhd2."PropertyAddress")
FROM "NashvilleHousingData" nhd2
WHERE nhd2."ParcelID" = nhd."ParcelID" AND
      nhd2."UniqueID" <> nhd."UniqueID"
WHERE nhd."PropertyAddress" IS NULL;

另外，COALESCE() 是多余的，因为已知值是 NULL：

    SET "PropertyAddress" = nhd2."PropertyAddress"