That will select (by a regex) every book which has a title starting with a number, is that what you want?

SELECT * FROM books WHERE title ~  ^[0-9] 

if you want integers which start with specific digits, you could use:

SELECT * FROM books WHERE CAST(price AS TEXT) LIKE  123% 

or use (if all your numbers have the same number of digits (a constraint would be useful then))

SELECT * FROM books WHERE price BETWEEN 123000 AND 123999;

PostgreSQL supports regular expressions matching.

So, your example would look like

SELECT * FROM books WHERE title ~  ^d+ ?  

This will match a title starting with one or more digits and an optional space

If you want to search as string, you can cast to text like this:

SELECT * FROM books WHERE price::TEXT LIKE  123% 

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]+ ;

Assuming that you re looking for "numbers that start with 7" rather than "strings that start with 7," maybe something like

select * from books where convert(char(32), book_id) like  7% 

Or whatever the Postgres equivalent of convert is.

I m late to the party here, but if you re dealing with integers of a fixed length you can just do integer comparison:

SELECT * FROM books WHERE price > 89999 AND price < 90100;

Which one of those is indexable?

This one is definitely btree-indexable:

WHERE title >=  0  AND title <  : 

Note that : comes after 9 in ASCII.

In PostreSQL you can use SIMILAR TO operator (more):

-- only digits
select * from books where title similar to  ^[0-9]*$ ;
-- start with digit
select * from books where title similar to  ^[0-9]%$ ;

For those who need to find all values that contain a number (regardless of its position) you can just use:

SELECT * FROM books WHERE title ~  [0-9] 

(tested with PostgreSQL 13.4)

If you are trying to use like for int column, use CAST to varchar.
(This is Objection RawFunction query example)

.where(
      db.obj.raw("CAST(id AS varchar)"),
      "like",
      `%${data.id}%`
    )