How to avoid null result of “SELECT max(rank) FROM test” for an empty table?

You can use COALESCE() along with aggregate function MAX() for this.

The syntax is as follows

SELECT COALESCE(MAX(`yourColumnName`), 0) FROM yourTableName;

To understand the above syntax, let us create a table. The query to create a table is as follows

mysql> create table avoidNullDemo
   -> (
   -> `rank` int
   -> );
Query OK, 0 rows affected (0.53 sec)

Insert some records in the table using insert command.

The query is as follows

mysql> insert into avoidNullDemo values(10);
Query OK, 1 row affected (0.20 sec)
mysql> insert into avoidNullDemo values(NULL);
Query OK, 1 row affected (0.18 sec)
mysql> insert into avoidNullDemo values(20);
Query OK, 1 row affected (0.17 sec)
mysql> insert into avoidNullDemo values(NULL);
Query OK, 1 row affected (0.11 sec)
mysql> insert into avoidNullDemo values(100);
Query OK, 1 row affected (0.11 sec)
mysql> insert into avoidNullDemo values(NULL);
Query OK, 1 row affected (0.16 sec)

Display you all records from the table using select statement.

The query is as follows

mysql> select *from avoidNullDemo;

The following is the output with NULL values

+------+
| rank |
+------+
| 10   |
| NULL |
| 20   |
| NULL |
| 100  |
| NULL |
+------+
6 rows in set (0.00 sec)

Here is the query to avoid null result

mysql> select COALESCE(MAX(`rank`), 0) FROM avoidNullDemo;

The following is the output

+--------------------------+
| COALESCE(MAX(`rank`), 0) |
+--------------------------+
| 100                      |
+--------------------------+
1 row in set (0.00 sec)

Here is the case when table is empty.

Let us delete all records from the above table.

The query is as follows

mysql> truncate table avoidNullDemo;
Query OK, 0 rows affected (0.92 sec)

Now the above table is empty. Let us implement the above query for empty table

mysql> select COALESCE(MAX(`rank`), 0) FROM avoidNullDemo;

The following is the output

+--------------------------+
| COALESCE(MAX(`rank`), 0) |
+--------------------------+
| 0                        |
+--------------------------+
1 row in set (0.00 sec)