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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?

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To differentiate between "put no data" and "put empty data", you can use NULL.

Another differences are as follows:

  • The LENGTH of an empty string is 0 and a LENGTH of NULL is NULL, 
  • NULLs will be sorted before the empty strings.
  • COUNT(message) can count empty strings but not NULLs.
  • By using a bound variable, you can search for an empty string but not for a NULL. 

Query:

SELECT  *

FROM    mytable 

WHERE   mytext = ?

In above query, whatever value you pass from the client it will never match a NULL in mytext, . 

To match NULLs, use below Query:

SELECT  *

FROM    mytable 

WHERE   mytext IS NULL

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