Question

我有一张桌子：

id1  |  date     |  idreff |
A11  | 2015-01-01| A11
B12  | 2016-02-03| A11
C53  | 2016-05-26| A11

ID1有一个IDreff。我想从日期中提取两种年龄： 1.交易年龄本身 2.第一笔交易的年龄，基于IDreff。

所以，我想要这个结果：

id1  |  date     |  idreff | Age of Transaction | Age IDreff

A11  | 2015-01-01| A11    
B12  | 2016-02-03| A11    
C53  | 2016-05-26| A11

如何在同一查询中获得两个查询（事务ID1和IDreff的年龄）的结果？

我试过这个：

SELECT *, age(t1.date) AS age1, age(t2.date) FROM table t1, table t2 WHERE t1.idreff=t2.id1

但结果并非如此，因为每行给我两倍。

Answer 1

您可以像这样修改您的SQL：

SELECT 
    t1.*, age(t1.date) AS age1, age(t1.date, t2.date) 
FROM 
    table t1, table t2 
WHERE 
    t1.idreff=t2.id1

Answer 2

你应该写更精确的连接：

SELECT 
    *, 
    age(t1.date) AS age1, 
    age(COALESCE(t2.date,t1.date)) as base_age
FROM 
    table t1
LEFT JOIN table t2 ON (t1.idreff=t2.id1 AND t1.id1<>t2.id1)
WHERE 1 = 1

Postgresql：从同一个表中查询

2 个答案: