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MYSQL NULL

Uses for NULL


.Data not yet known - such as end_date, rating
.Optional data - such as middle_initial (though that might be better as the empty string)
.0/0 - The result of certain computations, such as zero divided by zero.
.NULL is not equal to "" (blank string) or 0 (in case of integer).
.others?

Testing NULLs


.IS NULL / IS NOT NULL -- = NULL does not work like you expect.

.x <=> y is a "null-safe" comparison.
In a LEFT JOIN tests for rows of a for which there is not a corresponding row in b.


SELECT ...
 FROM a
 LEFT JOIN b ON ...
 WHERE b.id IS NULL


Conclusion

In this page (written and validated by ) you learned about MYSQL NULL . What's Next? If you are interested in completing MYSQL tutorial, your next topic will be learning about: MYSQL Limit and Offset.



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