MySQL checks whether a string is a number.

Delimiter $
Drop function if exists 'isnum' $
Create Function 'isnum' (STR varchar (25) returns int
Begin
Declare iresult int default 0;
If isnull (STR) then return 0; end if; -- Null String
If STR = ''then return 0; end if; -- Null String
Select STR Regexp '^ [0-9] * $ 'into iresult;
If iresult = 1 then
Return 1;
Else
Return 0;
End if;
End $
Delimiter;
For more information about delimiter, see the description of delimiter in MySQL function definition.
This function is used to determine whether a given string is a function. Usage example:
Select isnum ('12'); -- the result is 1
Select isnum ('12-'); -- the result is 0.
Select isnum (description) from table_xx

From http://blog.sina.com.cn/s/blog_69735aa501014cxo.html