mysql. How to select rows in a field that contains only numbers?

Question

MySQL

Let's say the table has a first_letter field, which can be either a number or a letter. How to select only those lines for which first_letter=number?

Answer 1

firstr_letter only one character?
test the following constructs for speed:
- WHERE first_letter IN (1,2,3,4,5,6,7,8,9,0)
- WHERE first_letter REGEXP '[0-9]'

Answer 2

something like this:
SELECT * FROM ... WHERE first_letter REGEXP '^[0-9]+$';
and if there is only one character, then you can simply
SELECT * FROM ... WHERE first_letter REGEXP '^[0-9]';

Answer 3

Regular expressions are not the best idea (see EXPLAIN).
select * from t where str<='9'
select * from t where str in ('0','1','2','3','4','5','6','7' ,'8','9')

Answer 4

Oh, you wrote.
SELECT * FROM x WHERE IS_NUMERIC(first_letter)

Answer 5

Does MySQL have the IS_NUMERIC.. function?