What happens if you do select 1 instead of a column name?

If you make SELECT 1 in an SQL query instead of specifying a column name, the result will be a set with one column, where all rows will have the value 1. This is often used to check for the existence of records or for test queries when the data from the table is not important, and you just need to get the rows.

Example:

SELECT 1 FROM users WHERE age > 30;

This query will return as many rows with the number 1 as there are users older than 30, but the user data itself will not be returned.