PostgreSQL中具有互换列值的行的聚合

Question

我的输入表看起来像这样

Source   Destn   Value
-----------------------
A        B        1
B        A        2

期望的输出 - ＆gt; A B 3

在PostgreSQL中获取上述结果的相应查询是什么？

Answer 1

试试这个：

SELECT CASE WHEN Source < Destn THEN Source ELSE Destn END,
       CASE WHEN Source >= Destn THEN Source ELSE Destn END,
       SUM(Value)
FROM mytable
GROUP BY CASE WHEN Source < Destn THEN Source ELSE Destn END,
         CASE WHEN Source >= Destn THEN Source ELSE Destn END

Demo here

修改：信用转到@Nick Barnes

可以使用LEAST和GREATEST简化查询：

SELECT least("Source","Destn"),
       greatest("Source","Destn"),
       SUM("Value")
FROM mytable
GROUP BY least("Source","Destn"),
         greatest("Source","Destn")

Demo here