在sql中命名输出答案

【问题标题】：naming the output in sql在sql中命名输出
【发布时间】：2020-04-06 17:29:35
【问题描述】：

我正在尝试命名我的查询输出，但我无法做到这是我的代码

select countryname , datemonth
from city, payments,State,country,dt_date,rooms,customer
where year(payments.PayDate) >"2010"  
ANd Payments.CustomerID = Customer.CustomerID
And State.CountryID = Country.CountryID
AND City.StateID = State.StateID
And Customer.CityID = City.CityID
and payments.DateID = dt_date.DateID 
union 
select countryname, datemonth
from city, payments,State,country,dt_date,rooms,booking,customer
where year(booking.DateBookingMade) >= "2010"
ANd booking.CustomerID = Customer.CustomerID
And State.CountryID = Country.CountryID
AND City.StateID = State.StateID
And Customer.CityID = City.CityID
and booking.DateID = dt_date.DateID;

我想将第一个选择命名为 payments，第二个选择命名为 booking 我的查询输出是

 countryname    datemonth
    UK           12
    USA          11
    UK            6
    UK            5
    USA           2

what I want is 

countryname    datemonth    status
    UK           12           payment
    USA          11           payment 
    UK            6           booking
    UK            5           booking
    USA           2           bookimg

感谢您的帮助

【问题讨论】：

标签： mysql sql olap

【解决方案1】：

为两个查询添加一个 3d 列：

select countryname , datemonth, 'payment' as status
.............................
union 
select countryname, datemonth, 'booking' as status
.............................

【讨论】：

【解决方案2】：

使用显式join 语法并避免逗号和大小写表达式以避免union all：

select countryname , datemonth,
       (case when year(p.paydte) > 2010 then 'payment' else 'booking' end)
from city c inner join
     payments p
     on  . . .  inner join
     State s
     on . . . inner join
     country cnt
     on . . . inner join 
     dt_date dt
     on . . .  inner join
     rooms r
     on . . . inner join
     customer cst
     . . .
where year(p.PayDate) >= 2010;

【讨论】：