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MySQL NULL Values

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We have seen the SQL SELECT command along with the WHERE caluse to fetch data from a MySQL table, but when we try to give a condition, which compares the field or column value to NULL, it does not work properly.
To handle this type of situation, MySQL provides three operators-

  • IS NULL –  This operator returns true, if the column value is NULL.
  • IS NOT NULL – This operator  returns true, if the column value is not NULL.
  • <=> – This operator compares values, which (unlike the = operator) is true even for two NULL values.

The conditions involving NULL are special. You can’t  use = NULL or !=NULL to look for NULL values in columns. Such comparisons always fail because it is  impossible to tell wheteher they are true or not. Some- times, even NULL=NULL fails.
To look for columns that are or are not NULL, use IS NULL or IS NOT NULL.

For Examples

Table tblstudents

id Name Roll_no Class
1 Anuj kumar 10806121 B.tech
2 Sanjeev 10883327 NULL
3 Amit 13123121 BA
4 Rahul 23424323 NULL

Handling NULL values
Ex:

Select * from tblstudents where Class IS NULL;

OUTPUT

id Name Roll_no Class
2 Sanjeev 10883327 NULL
4 Rahul 23424323 NULL

Ex:

Select * from tblstudents where Class IS NOT NULL;

OUTPUT

id Name Roll_no Class
1 Anuj kumar 10806121 B.tech
3 Amit 13123121 BA

NOTE :

You can see  that = and != do not work with the NULL Values.

Select * from tblstudents where Class=NULL;
Select * from tblstudents where Class!=NULL;
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