使用mysql将两列视为一

Question

我有一张桌子，上面有两笔付款，每笔都有自己的日期，就像这样：

table
______________
id
.......
payment1
payment1_date
payment2
payment2_date

我需要的是付款的有序列表，而忽略是付款1还是付款2。

付款既可以是空的，也可以是一次，也可以全部填充。

结果如下：

id        payments      date         ... 
3         (payment1)    2018-08-01
5         (payment2)    2018-08-03
4         (payment2)    2018-08-04
3         (payment2)    2018-08-07

付款1将是预付款，其余的将是付款2，但对于会计信息，我只想显示按日期排序的所有付款，即付款日期x_date

Answer 1

我会尝试的：

    select id,payment1 as payment, payment1_date as payment_date
    from table
    where payment1 is not null or payment1 <> ''
    union 
    select id,payment2 as payment, payment2_date as payment_date
    from table
    where payment2 is not null or payment2 <> ''
    order by 3