MySQL, better to insert NULL or empty string?

roflwaffle picture roflwaffle · Aug 12, 2009 · Viewed 93.7k times · Source

I have a form on a website which has a lot of different fields. Some of the fields are optional while some are mandatory. In my DB I have a table which holds all these values, is it better practice to insert a NULL value or an empty string into the DB columns where the user didn't put any data?

Answer

Quassnoi picture Quassnoi · Aug 12, 2009

By using NULL you can distinguish between "put no data" and "put empty data".

Some more differences:

  • A LENGTH of NULL is NULL, a LENGTH of an empty string is 0.

  • NULLs are sorted before the empty strings.

  • COUNT(message) will count empty strings but not NULLs

  • You can search for an empty string using a bound variable but not for a NULL. This query:

    SELECT  *
    FROM    mytable 
    WHERE   mytext = ?
    

    will never match a NULL in mytext, whatever value you pass from the client. To match NULLs, you'll have to use other query:

    SELECT  *
    FROM    mytable 
    WHERE   mytext IS NULL