Question

我正在尝试将一个表中的值设置为另一个表中值的总和。这些方面的东西：

UPDATE table1
SET field1 = SUM(table2.field2)
FROM table1
INNER JOIN table2 ON table1.field3 = table2.field3
GROUP BY table1.field3

当然，如果这样，它将无效 - SET不支持SUM，并且不支持GROUP BY。

我应该知道这一点，但我的想法是空白的。我做错了什么？

Answer 1

UPDATE t1
SET t1.field1 = t2.field2Sum
FROM table1 t1
INNER JOIN (select field3, sum(field2) as field2Sum
   from table2
  group by field3) as t2
on t2.field3 = t1.field3

Answer 2

使用：

UPDATE table1
   SET field1 = (SELECT SUM(t2.field2) 
                   FROM TABLE2 t2 
                  WHERE t2.field3 = field2)

Answer 3

或者您可以混合使用JBrooks和OMG Ponies个答案：

UPDATE table1
   SET field1 = (SELECT SUM(field2)
                   FROM table2 AS t2
                  WHERE t2.field3 = t1.field3)
  FROM table1 AS t1

Answer 4

使用CROSS APPLY的好情况

UPDATE t1
   SET t1.field1 = t2.field2Sum
  FROM table1 t1
 CROSS APPLY (SELECT SUM(field2) as field2Sum
                FROM table2 t2
               WHERE t2.field3 = t1.field3) AS t2

Answer 5

我知道问题是标记为SQL Server，但如果使用 PostgreSQL ，请注意UPDATE和JOIN。 @JBrooks回答没有工作：

UPDATE t1
SET t1.field1 = t2.field2Sum
FROM table1 t1
INNER JOIN (...) as t2
on t2.field3 = t1.field3

您必须将其改编为：

UPDATE table1 t1
SET t1.field1 = t2.field2Sum
FROM (...) as t2
WHERE t2.field3 = t1.field3

请参阅文档中的参数from_list，了解PostgreSQL将FROM视为自我加入的原因：https://www.postgresql.org/docs/9.5/static/sql-update.html#AEN89239

Answer 6

您还可以像下面那样使用CTE。

;WITH t2 AS (
    SELECT field3, SUM(field2) AS field2
    FROM table2
    GROUP BY field3
)
UPDATE table1
SET table1.field1 = t2.field2
FROM table1
INNER JOIN t2 ON table1.field3 = t2.field3

SQL更新查询中的聚合函数？

6 个答案: