Você pode querer criar uma função definida pelo usuário que corresponda ao valor em relação a uma expressão regular:
CREATE FUNCTION IsNumeric (sIn varchar(1024)) RETURNS tinyint
RETURN sIn REGEXP '^(-|\\+){0,1}([0-9]+\\.[0-9]*|[0-9]*\\.[0-9]+|[0-9]+)$';
Fonte:MySQL Forums ::Microsoft SQL Server ::IsNumeric( ) cláusula no MySQL?
Testes de verdade:
mysql> SELECT ISNUMERIC('1');
+----------------+
| ISNUMERIC('1') |
+----------------+
| 1 |
+----------------+
1 row in set (0.01 sec)
mysql> SELECT ISNUMERIC(25);
+---------------+
| ISNUMERIC(25) |
+---------------+
| 1 |
+---------------+
1 row in set (0.00 sec)
mysql> SELECT ISNUMERIC('-100');
+-----------------+
| ISNUMERIC(-100) |
+-----------------+
| 1 |
+-----------------+
1 row in set (0.03 sec)
mysql> SELECT ISNUMERIC('1.5');
+------------------+
| ISNUMERIC('1.5') |
+------------------+
| 1 |
+------------------+
1 row in set (0.00 sec)
mysql> SELECT ISNUMERIC('-1.5');
+-------------------+
| ISNUMERIC('-1.5') |
+-------------------+
| 1 |
+-------------------+
1 row in set (0.02 sec)
Testes falsos:
mysql> SELECT ISNUMERIC('a');
+----------------+
| ISNUMERIC('a') |
+----------------+
| 0 |
+----------------+
1 row in set (0.02 sec)
mysql> SELECT ISNUMERIC('a1');
+-----------------+
| ISNUMERIC('a1') |
+-----------------+
| 0 |
+-----------------+
1 row in set (0.00 sec)
mysql> SELECT ISNUMERIC('10a');
+------------------+
| ISNUMERIC('10a') |
+------------------+
| 0 |
+------------------+
1 row in set (0.00 sec)
mysql> SELECT ISNUMERIC('0.a');
+------------------+
| ISNUMERIC('0.a') |
+------------------+
| 0 |
+------------------+
1 row in set (0.00 sec)
mysql> SELECT ISNUMERIC('a.0');
+------------------+
| ISNUMERIC('a.0') |
+------------------+
| 0 |
+------------------+
1 row in set (0.00 sec)
