SQL LIKE condition to check for integer?

Question

I am using a set of SQL LIKE conditions to go through the alphabet and list all items beginning with the appropriate letter, e.g. to get all books where the title starts wit

Answer 1

Tested on PostgreSQL 9.5 :

-- only digits

select * from books where title ~ '^[0-9]*$';

or,

select * from books where title SIMILAR TO '[0-9]*';

-- start with digit

select * from books where title ~ '^[0-9]+';