Null not null mysql

The NOT logical operator is used to test for Boolean conditions and returns true if the condition is false. The NOT operator returns false if the condition been tested is true. There will be cases when we will have to perform computations on a query result set and return the values.

Performing any arithmetic operations on columns that have the NULL value returns null results. In order to avoid such situations from happening, we can employ the use of the NOT NULL clause to limit the results on which our data operates.

The employee number should always be supplied. The basic syntax when null is used as a keyword is as follows. Continuing with the example above , suppose we need details of members whose contact number is not null. Improve this answer. Alex Tartan Alex Tartan 6, 10 10 gold badges 34 34 silver badges 42 42 bronze badges.

Otherwise, it returns expr3. Show 6 more comments. Carlos Torres Carlos Torres 1 1 gold badge 9 9 silver badges 19 19 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.

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Asked 12 years, 2 months ago. Active 1 year, 3 months ago. Viewed 48k times. And when should they be used?

Improve this question. It is a very classic question. Add a comment. Active Oldest Votes. NULL means you do not have to provide a value for the field Improve this answer. Sparky Sparky Simplest answer anyone could've given.

I have noticed this seems to not make sense to some programmers, but that is how it works. AirThomas You and I have described the exact same mechanism in nearly the same way. If you find you have a table with lots of columns many of which can be NULL, that starts sounding like an antipattern, consider whether vertical partitioning makes more sense in your application context : There is another useful use for NULL - making all the columns in an index NULL will stop an index record being created for that row, which optimises indexes; you may want to index only a very small subset of rows e.

MarkR MarkR Amber Amber k 78 78 gold badges silver badges bronze badges. Alex Martelli Alex Martelli k gold badges silver badges bronze badges. In some cases, you may want the safeguard for most of the rows, but there are exceptions.