获取最短日期作为条件

Question

我有一个表包含所有电话号码的发票，每个号码有几个发票，我想只显示精确数字的第一张发票，但我真的不知道如何只获得第一张发票，这是我的查询

SELECT 
    b.contrno 
    a.AR_INVDATE 
    FROM P_STG_TABS.IVM_INVOICE_RECORD a 

    INNER JOIN P_EDW_TMP.invoice b 
    ON b.contrno=a.contrno 

    WHERE a.AR_INVDATE< (SELECT AR_INVDATE FROM P_STG_TABS.IVM_INVOICE_RECORD WHERE contrno=b.contrno ) 

Answer 1

使用ROW_NUMBER()：

SELECT 
    t.contrno, 
    t.AR_INVDATE 
FROM 
(
    SELECT 
     b.contrno, 
     a.AR_INVDATE, 
     ROW_NUMBER() OVER (PARTITION BY b.contrno ORDER BY a.AR_INVDATE) rn 
    FROM P_STG_TABS.IVM_INVOICE_RECORD a 
    INNER JOIN P_EDW_TMP.invoice b 
     ON b.contrno = a.contrno 
) t 
WHERE t.rn = 1; 

如果你担心联系，要显示所有的联系，那么你就可以无论RANK或DENSE_RANK更换ROW_NUMBER。

Answer 2

如果我正确理解，再一个方法是使用group by与min(a.AR_INVDATE)：

SELECT 
b.contrno, 
min(a.AR_INVDATE) 
FROM P_STG_TABS.IVM_INVOICE_RECORD a 
INNER JOIN P_EDW_TMP.invoice b 
ON b.contrno=a.contrno 
group by b.contrno 

Answer 3

Teradata的支持QUALIFY子句来过滤OLAP-函数的结果（类似于HAVINGGROUP BY之后），从而大大简化添Biegeleisens的回答是：

SELECT * 
FROM P_STG_TABS.IVM_INVOICE_RECORD a 
INNER JOIN P_EDW_TMP.invoice b 
    ON b.contrno = a.contrno 
QUALIFY 
    ROW_NUMBER() 
    OVER (PARTITION BY b.contrno 
     ORDER BY a.AR_INVDATE) = 1 

另外，你可以将ROW_NUMBER在连接前（可能是取决于附加条件更有效）：

SELECT * 
FROM 
(SELECT * 
    FROM P_STG_TABS.IVM_INVOICE_RECORD a 
    QUALIFY 
     ROW_NUMBER() 
     OVER (PARTITION BY b.contrno 
      ORDER BY a.AR_INVDATE) = 1 
) AS a 
INNER JOIN P_EDW_TMP.invoice b 
    ON b.contrno = a.contrno