Following is example of SQL database query
SELECT * FROM suppliersWHERE supplier_name not like 'T%';
WHERE supplier_name not like 'T%';
This query will returns the records where supplier_name does not starts with T
But how can I achieve the same functionality in salesforce?
There's no select *, so you have to specify the exact fields to query, you'd then use NOT and LIKE, e.g.
SELECT id,name, otherFields from suppliers where NOT supplier_name like 'T%'