MySQL query to find single value from duplicates with certain condition by excluding other records using NOT IN

Let us first create a table −

mysql> create table DemoTable
(
   Id int,
   FirstName varchar(100)
);
Query OK, 0 rows affected (0.69 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable values(100,'Chris');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values(100,'Robert');
Query OK, 1 row affected (0.48 sec)
mysql> insert into DemoTable values(100,'Mike');
Query OK, 1 row affected (0.23 sec)
mysql> insert into DemoTable values(100,'Sam');
Query OK, 1 row affected (0.48 sec)
mysql> insert into DemoTable values(101,'David');
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable values(101,'Robert');
Query OK, 1 row affected (0.44 sec)
mysql> insert into DemoTable values(210,'Chris');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values(210,'Bob');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values(210,'Sam');
Query OK, 1 row affected (0.17 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+------+-----------+
| Id   | FirstName |
+------+-----------+
|  100 | Chris     |
|  100 | Robert    |
|  100 | Mike      |
|  100 | Sam       |
|  101 | David     |
|  101 | Robert    |
|  210 | Chris     |
|  210 | Bob       |
|  210 | Sam       |
+------+-----------+
9 rows in set (0.00 sec)

Here is the query to find a single value from duplicates with certain condition −

mysql> select distinct Id from DemoTable
where Id not in
(
   select Id from DemoTable where FirstName='Chris'
);

This will produce the following output −

+------+
| Id   |
+------+
| 101  |
+------+
1 row in set (0.08 sec)