MySQL query to calculate the days between two dates from different columns but similar rows

Let us first create a table −

mysql> create table DemoTable1471
   -> (
   -> EmployeeJoiningDate date,
   -> EmployeeRelievingDate date
   -> );
Query OK, 0 rows affected (0.57 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1471 values('2018-06-21','2018-12-21');
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable1471 values('2017-01-19','2019-01-31');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable1471 values('2015-12-31','2016-03-01');
Query OK, 1 row affected (0.11 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1471;

This will produce the following output −

+---------------------+-----------------------+
| EmployeeJoiningDate | EmployeeRelievingDate |
+---------------------+-----------------------+
| 2018-06-21          |          2018-12-21   |
| 2017-01-19          |          2019-01-31   |
| 2015-12-31          |          2016-03-01   |
+---------------------+-----------------------+
3 rows in set (0.00 sec)

Here is the query to calculate the days between two dates −

mysql> select datediff(EmployeeRelievingDate,EmployeeJoiningDate) as EmployeeWorkDays from DemoTable1471;

This will produce the following output −

+------------------+
| EmployeeWorkDays |
+------------------+
|              183 |
|              742 |
|               61 |
+------------------+
3 rows in set (0.00 sec)