基於主查詢列的子查詢

Question

我正在尋求幫助，根據 table1 中的列在 table2 上使用子查詢構建 SQL 查詢，但 table1 和 table2 沒有關系。

就像是

SELECT name, address, dateCreated,
(SELECT itemId FROM table2 WHERE itemDate BETWEEN dateCreated AND DATEADD(ss,10,dateCreated) as item
FROM table1

因此，對於每一行，必須根據該行的 dateCreated 從 table2 中選擇“項目”。

Answer 1

您可以嘗試使用IF EXISTS ，如下所示。

SELECT name
    , [address]
    , dateCreated
FROM table1
where exits(
    SELECT itemId 
    FROM table2 WHERE itemDate BETWEEN dateCreated AND DATEADD(ss, 10,dateCreated) and table1.ItemId = table2.ItemId)

Answer 2

SELECT name, address, dateCreated, table2.itemId 
from table1 LEFT JOIN  table2  WHERE   itemDate BETWEEN dateCreated AND DATEADD(ss,10,dateCreated) 

Answer 3

如果您最多需要table2一項，那么您的方法很好，但您想要top (1) ：

SELECT t1.name, t1.address, t1.dateCreated,
       (SELECT TOP (1) t2.itemId
        FROM table2 t2
        WHERE t2.itemDate BETWEEN t1.dateCreated AND DATEADD(second, 10, t1.dateCreated
       ) as item
FROM table1 t1;

您也可以將其表述為橫向連接，使用outer apply ：

SELECT t1.name, t1.address, t1.dateCreated,
       t2.itemId
FROM table1 t1 OUTER APPLY
     (SELECT TOP (1) t2.itemId
      FROM table2 t2
      WHERE t2.itemDate BETWEEN t1.dateCreated AND DATEADD(second, 10, t1.dateCreated
     ) t2;

這使得選擇多個列變得容易。

Answer 4

你能試試下面的邏輯嗎？ 如果在 table2 中針對 table1 中的任何行找到多個記錄，則嘗試的方法將通過 ERROR。

SELECT A.name, 
A.address, 
A.dateCreated,
B.itemId 
FROM table1 A
INNER JOIN table2 B
ON B.itemDate  BETWEEN A.dateCreated AND DATEADD(ss,10,A.dateCreated)

通過上述查詢，您將根據應用於 Date --BETWEEN A.dateCreated AND DATEADD(ss,10,A.dateCreated) 的邏輯為 table1 中的每一行獲得 N 行數