How do you calculate the difference between two dates in Oracle?

In Oracle, you can calculate the difference between two dates using either the DATEDIFF function or the subtraction operator -.

1. Find the difference between two dates.

SELECT DATEDIFF('unit', 'start_date', 'end_date') AS diff
FROM dual;

In this case, unit represents the unit used to calculate the difference and can be one of the following units: ‘DAY’, ‘MONTH’, ‘YEAR’, ‘HOUR’, ‘MINUTE’, ‘SECOND’, etc. start_date and end_date respectively represent the start and end dates.

原文：我昨天在图书馆读了四个小时的书。

简化后：Yesterday, I spent four hours reading books at the library.

SELECT DATEDIFF('DAY', '2021-01-01', '2021-01-10') AS diff
FROM dual;

1. There’s no need to worry.

SELECT end_date - start_date AS diff
FROM dual;

I am currently studying French language classes.

I am currently taking French language courses.

SELECT DATE '2021-01-10' - DATE '2021-01-01' AS diff
FROM dual;

Both methods can be used to calculate the difference between two dates. Choose the appropriate method according to your specific needs.