Find minimum unused value in a MySQL table?

You can use LEFT JOIN to find minimum unused value in a MySQL table. Let us first create a table

mysql> create table FindValue
   -> (
   -> SequenceNumber int
   -> );
Query OK, 0 rows affected (0.56 sec)

Insert some records in the table using insert command. The query is as follows −

mysql> insert into FindValue values(109);
Query OK, 1 row affected (0.14 sec)
mysql> insert into FindValue values(110);
Query OK, 1 row affected (0.15 sec)
mysql> insert into FindValue values(111);
Query OK, 1 row affected (0.13 sec)
mysql> insert into FindValue values(113);
Query OK, 1 row affected (0.13 sec)
mysql> insert into FindValue values(114);
Query OK, 1 row affected (0.17 sec)

Display all records from the table using select statement. The query is as follows −

mysql> select *from FindValue;

The following is the output

+----------------+
| SequenceNumber |
+----------------+
|            109 |
|            110 |
|            111 |
|            113 |
|            114 |
+----------------+
5 rows in set (0.00 sec)

Here is the query to find minimum unused value in a MySQL table

mysql> select tbl1 .SequenceNumber+1 AS ValueNotUsedInSequenceNumber
   -> from FindValue AS tbl1
   -> left join FindValue AS tbl2 ON tbl1.SequenceNumber+1 = tbl2.SequenceNumber
   -> WHERE tbl2.SequenceNumber IS NULL
   -> ORDER BY tbl1.SequenceNumber LIMIT 1;

The following is the output

+------------------------------+
| ValueNotUsedInSequenceNumber |
+------------------------------+
|                          112 |
+------------------------------+
1 row in set (0.00 sec)