MySQL queries to update date records with NULL values

You can use IFNULL() for this. Let us first create a table −

mysql> create table DemoTable
   -> (
   -> added_date date,
   -> updated_date date
   -> );
Query OK, 0 rows affected (0.95 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values('2019-01-10','2019-06-01');
Query OK, 1 row affected (0.19 sec)

mysql> insert into DemoTable values('2019-05-19',NULL);
Query OK, 1 row affected (0.14 sec)

mysql> insert into DemoTable values(NULL,'2019-09-05');
Query OK, 1 row affected (0.18 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+------------+--------------+
| added_date | updated_date |
+------------+--------------+
| 2019-01-10 | 2019-06-01   |
| 2019-05-19 | NULL         |
| NULL       | 2019-09-05   |
+------------+--------------+
3 rows in set (0.00 sec)

Case 1 − If you want the result in descending order.

Here is the query to select row with added_date and updated_date.

mysql> select *from DemoTable order by ifnull(updated_date,added_date) desc;

This will produce the following output −

+------------+--------------+
| added_date | updated_date |
+------------+--------------+
| NULL       | 2019-09-05   |
| 2019-01-10 | 2019-06-01   |
| 2019-05-19 | NULL         |
+------------+--------------+
3 rows in set (0.00 sec)

Case 2 − If you want the result in ascending order.

Here is the query to select row with added_date and updated_date −

mysql> select *from DemoTable order by ifnull(updated_date,added_date);

This will produce the following output −

+------------+--------------+
| added_date | updated_date |
+------------+--------------+
| 2019-05-19 | NULL         |
| 2019-01-10 | 2019-06-01   |
| NULL       | 2019-09-05   |
+------------+--------------+
3 rows in set (0.00 sec)