Question

我有postgresql问题，我认为这很简单，但我无法概念化实现此目的所需的连接。

我有一个这种格式的表：

Company    Agreement_num    End_of_Agreement    Contract_Amount
ABC             2               (null)              (null)
ABC           (null)          2015-01-10              10
ABC           (null)          2015-09-01              12
ACME            2               (null)              (null)
ACME          (null)          2014-06-05               5

我希望桌子看起来像这样：

Company    Agreement_num    End_of_Agreement    Contract_Amount
ABC             2               (null)              (null)
ABC             2             2015-01-10              10
ABC             2             2015-09-01              12
ACME            2               (null)              (null)
ACME            2             2015-06-05               5

基本上，只需将Agreement_num插入相应的公司。

为了让你知道我要去哪里，在此之后，我会做一个WHERE子句来只抓取那些没有达到End_of_Agreement的行：

Company   Agreement_num     End_of_Agreement    Contract_Amount
ABC             2              2015-09-01             12
ACME            2              2015-06-05              5

谢谢！

Answer 1

我认为你可以使用类似的东西：

SELECT
    t1.Company,
    t2.Agreement_num,
    t1.End_Of_Agreement, 
    t1.Contract_Amount
FROM
    table
    INNER JOIN 
        (
            SELECT company, agreement_num
            FROM table
            WHERE agreement_num IS NOT NULL
        ) t2 ON
        t1.company = t2.company

子查询将获取每个公司的agreement_num并在主查询中使用它。

您还可以使用窗口函数将其拉出来，从而缩小查询范围：

SELECT
  company,
  MAX(agreement_num) OVER (PARTITION BY company) as agreement_num,
  end_of_agreement,
  contract_amount
FROM 
  table;

Here's a sqlfiddle showing this

Answer 2

我认为你不想加入，我认为你需要使用MAX这样的聚合函数：

SELECT
  Company,
  MAX(Agreement_num) AS Agreement_num,
  MAX(End_of_Agreement) AS End_of_Agreement,
  MAX(Contract_Amount) AS Contract_Amount
FROM
  yourtable
GROUP BY
  Company

但不清楚Contract_Amount是否总是在增加。如果不是，并且您想要返回与最后一个End_Of_Aggreement关联的Contract_Amount，则可以将窗口函数与DISTINCT ON结合使用：

SELECT DISTINCT ON (company)
  company,
  MAX(Agreement_num) OVER (PARTITION BY Company) AS Agreement_num,
  End_of_Agreement,
  Contract_Amount
FROM
  yourtable
ORDER BY
  company,
  end_of_agreement DESC NULLS LAST

加入需要的帮助

2 个答案: