如何计算日期之间的天数

Question

我目前正在做一个项目，我正在寻找输出，我需要计算预约和手术之间的天数，目前我有这个

Select Patient_FirstName ||' '|| Patient_surname "Patient Name", appointment_date, OPeration_date, datediff(Appointment_Date,Operation_Date) "Days till operation"
from PatientRecord p , Patient b, Appointment a, Operation o
where p.patient_ID = b.Patient_ID
and p.appointment_ID = a.appointment_ID
and p.operation_ID = o.OPeration_ID
order by Patient_Surname;

这只是返回一个无效的标识符，

当我整整几个月时它工作正常，但我需要几天

Select Patient_FirstName ||' '|| Patient_surname "Patient Name", appointment_date, OPeration_date, Round (months_between(Appointment_Date,Operation_Date)) "Days till operation"
from PatientRecord p , Patient b, Appointment a, Operation o
where p.patient_ID = b.Patient_ID
and p.appointment_ID = a.appointment_ID
and p.operation_ID = o.OPeration_ID
order by Patient_Surname;

这就是我四舍五入的时间，我可以几天做类似的事情吗？

Answer 1

首先，从不在FROM 子句中使用逗号。 始终使用正确、明确的JOIN 语法。

在 Oracle 中，您可以只减去日期：

Select Patient_FirstName ||' '|| Patient_surname as "Patient Name",
       appointment_date, Operation_date,
       trunc(Operation_Date - Appointment_Date) as "Days till operation"
from PatientRecord pr join
     Patient p
     on pr.patient_ID = p.Patient_ID join
     Appointment a
     on pr.appointment_ID = a.appointment_ID join
     Operation o
     on pr.operation_ID = o.Operation_ID
order by Patient_Surname;

Answer 2

如果appointment_date 是2017-01-01 14:30:00 而operation_date 是2017-01-04 09:30:00，那么差异是2 天21 小时，但您可能希望将其作为2017-01-01 和2017-01-04 之间的差异进行比较显示为 3 天（而不是 2 天）所以：

Select Patient_FirstName ||' '|| Patient_surname AS "Patient Name",
       appointment_date,
       OPeration_date,
       TRUNC( Operation_Date ) - TRUNC ( Appointment_Date ) AS "Days till operation"
from   PatientRecord p
       INNER JOIN Patient b
       ON ( p.patient_ID = b.Patient_ID )
       INNER JOIN Appointment a
       ON ( p.appointment_ID = a.appointment_ID )
       INNER JOIN Operation o
       ON ( p.operation_ID = o.OPeration_ID )
order by Patient_Surname;

你也可以使用：

CEIL( Operation_Date - Appointment_Date ) AS "Days till operation"

Answer 3

试试这个：

Select DateDiff(d,Appointment_Date,Operation_Date) as [Days till operation]