分組時避免多個子選擇

Question

我有一個查詢，其工作方式如下：

select table_one.x, sum(table_one.y)
(select foo from table_two where table_one.x = table_two.x) as item_description
from table_one
inner join table_two
on table_one.x = table_two.x
-- where table_2 row has various attributes
group by table_one.x

分組意味着我需要一個子選擇來訪問表二中的 foo。 現在，如果我想從表二中選擇第二列，有沒有辦法在沒有第二個子選擇的情況下訪問它？

數據庫是 DB2。

編輯：join 是多對一的，即將 table_one 視為訂單，將 table_b 視為包含該項目的信息。

Answer 1

table_two 對每個 table_one.x 是否有多行或者是一對二連接...如果是一對二連接，那么這是否不符合您的要求...因為您的子選擇是在與您的加入條件相同

SELECT
   table_one.x, table_two.foo, sum(table_one.y)
FROM table_one
   INNER JOIN table_two
       ON table_one.x = table_two.x 
GROUP BY
   table_one.x, table_two.foo

Answer 2

SELECT  *
FROM    (
        SELECT  x, SUM(y)
        FROM    table_one
        GROUP BY
                x
        ) AS t1
INNER JOIN
        table_two t2
ON      t2.x = t1.x
-- where table_2 row has various attributes