mysql - 选择查询中获取的两列的差异

Question

我已获取两列 checkin_date 和 booking_time ，如下所示。我如何获得由此创建的两列的差异？

SELECT CAST(CONCAT(MID(Checkin,7,4) , '-' 
  , MID(Checkin,1,2)  , '-' 
  , MID(Checkin,4,2))
 AS DATETIME) as Checkin_Date,

 CAST(CONCAT(MID(Book_Time,7,4) , '-' 
  , MID(Book_Time,1,2)  , '-' 
  , MID(Book_Time,4,2))
 AS DATETIME) as Booking_Date

FROM rl_transactional.mydb

我尝试在 FROM rl_transactional.mydb 之前执行 Checkin_Date - Booking_Date，但出现错误

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'Checkin_Date - Booking_Date FROM rl_transactional.mydb' at line 16

编辑:根据建议，我使用了以下查询

SELECT CAST(CONCAT(MID(Checkin,7,4) , '-' 
  , MID(Checkin,1,2)  , '-' 
  , MID(Checkin,4,2))
 AS DATETIME) as Checkin_Date, 

CAST(CONCAT(MID(CheckOut,7,4) , '-' 
  , MID(CheckOut,1,2)  , '-' 
  , MID(CheckOut,4,2))
 AS DATETIME) as CheckOut_Date,

 CAST(CONCAT(MID(Book_Time,7,4) , '-' 
  , MID(Book_Time,1,2)  , '-' 
  , MID(Book_Time,4,2))
 AS DATETIME) as Booking_Date,

Checkin_Date - Booking_Date
from (
    SELECT CAST(CONCAT(MID(Checkin,7,4) , '-' 
      , MID(Checkin,1,2)  , '-' 
      , MID(Checkin,4,2))
     AS DATETIME) as Checkin_Date,
     CAST(CONCAT(MID(Book_Time,7,4) , '-' 
      , MID(Book_Time,1,2)  , '-' 
      , MID(Book_Time,4,2))
     AS DATETIME) as Booking_Date
    FROM rl_transactional.mydb
) c,
FROM rl_transactional.mydb

我遇到以下错误

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'Checkin_Date - Booking_Date from ( SELECT CAST(CONCAT(MID(Checkin,7,4) , '-'' at line 1

Answer 1

尝试运行以下查询:

SELECT 
     c.Checkin_Date, 
     c.CheckOut_Date
     c.Booking_Date,
     c.Checkin_Date - c.Booking_Date
from (
    SELECT CAST(CONCAT(MID(Checkin,7,4) , '-' 
      , MID(Checkin,1,2)  , '-' 
      , MID(Checkin,4,2))
     AS DATETIME) as Checkin_Date,
     CAST(CONCAT(MID(Book_Time,7,4) , '-' 
      , MID(Book_Time,1,2)  , '-' 
      , MID(Book_Time,4,2))
     AS DATETIME) as Booking_Date,
     CAST(CONCAT(MID(CheckOut,7,4) , '-' 
      , MID(CheckOut,1,2)  , '-' 
      , MID(CheckOut,4,2))
     AS DATETIME) as CheckOut_Date
    FROM rl_transactional.mydb
) c;