替代SQL中的子查询吗？

时间：2019-02-27 12:23:42

标签： sql sql-server-2008 subquery

我有应返回少量列结果的查询。还有一个要求，我必须对其中一列应用其他过滤器。我发现使用子查询（在主选择内选择）的解决方案是示例：

SELECT 
   recid,
   price,
   receive_date,
   (SELECT deduction FROM Cost WHERE recid = c.recid AND status = 'Y') AS deduction
FROM Cost c
   INNER JOIN cost_types ct
      c.recid = ct.recid
WHERE cost_year = '2018'

上面的查询必须从Cost表中提取与cost_type表记录匹配且cost_year是2018的所有记录。最重要的是，我必须提交deduction，其中status是Y。我想知道我可以使用什么其他技术进行此查询？我知道UNION / UNION ALL，但这是更多代码，似乎很多余。如果有人有建议或更好的方法来解决这种情况，请告诉我。另外，我想知道这是否更适合存储过程？会推荐吗？

2 个答案:

答案 0 :(得分：1)

JOIN是正常的方法，如下所示：

SELECT c.recid, c.price, c.receive_date,
       cd.deduction
FROM cost c INNER JOIN
     cost_types ct
     ON c.recid = ct.recid LEFT JOIN
     cost cd
     ON cd.recid = c.recid AND cd.status = 'Y'
WHERE c.cost_year = 2018;

这是在猜测列的来源。如果这些列来自不同的表，请调整限定词。

您可能还可以使用窗口功能：

SELECT c.recid, c.price, c.receive_date,
       SUM(CASE WHEN c.status = 'Y' THEN c.deduction END) OVER (PARTITION BY c.recid) as deduction
FROM cost c INNER JOIN
     cost_types ct
     ON c.recid = ct.recid 
WHERE c.cost_year = 2018;

答案 1 :(得分：0)

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CASE

编辑：：我怀疑您想要一些东西：

SELECT recid, price, receive_date,
      (CASE WHEN status = 'Y' THEN deduction END) AS deduction
FROM Cost c INNER JOIN 
     cost_types ct
     ON c.recid = ct.recid 
WHERE cost_year =  2018;
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