roflwaffle roflwaffle - 1 month ago 6
MySQL Question

MySQL, better to insert NULL or empty string?

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

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
    
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