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Connor McDonald

Thanks for the question.

Asked: January 10, 2022 - 6:29 am UTC

Last updated: January 11, 2022 - 3:48 am UTC

Version: mysql 8.0.22

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You Asked

Does MySql Btree index store NULL value?I execute a sql like "explain select * from t1 where id is null",most id of table t1 is NULL, I think it should use full table scan instead of index scan. But MySql use index. why?

and Chris said...

We specialize in Oracle Database here. If you need detailed help with MySQL, then a forum such as the MySQL Community Space is a better place to ask.

That said, the MySQL docs answer your question:

MySQL can perform the same optimization on col_name IS NULL that it can use for col_name = constant_value. For example, MySQL can use indexes and ranges to search for NULL with IS NULL.

https://dev.mysql.com/doc/refman/8.0/en/is-null-optimization.html

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Comments

MHESH, January 10, 2022 - 7:14 pm UTC

How to check user tables has primary key or not

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