SQL queries the sum of two values as a condition

Purpose: To filter the sum of two fields in a table as a where condition

Querying for records with no expiration
Select a, from Test where a+b>now ();//A: Deposit time B: Validity period   

SQL will error when you make the above query.

However, simply put the above SQL into the code and replace now () with the method of the current timestamp obtained by the corresponding language (e.g. time () in PHP), execute, perfect ok!

Analysis: Running this way directly in SQL, SQL will understand now () as the current format time, so after a+b directly understand the normal string, not the concept of the time stamp understood, so that the operation did not get the desired result.

This understanding may not be correct, there is a better answer welcome comment exchange!

SQL queries the sum of two values as a condition