[sql] querying WHERE condition to character length?

I have a database with a large number of words but i want to select only those records where the character length is equal to a given number (in example case 3):

$query = ("SELECT * FROM $db WHERE conditions AND length = 3");

But this does not work... can someone show me the correct query?

I think you want this:

select *
from dbo.table
where DATALENGTH(column_name) = 3

SELECT *
   FROM   my_table
   WHERE  substr(my_field,1,5) = "abcde";