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This article mainly introduces when the MySQL database needs to use the index, the article is very detailed, has a certain reference value, interested friends must read it!

When do you need to use an index?

(1) columns are often used in where conditions.

(2) there are a large number of null values in the column

(3) the table has hardly been modified.

(4) the amount of data is so large that only 2-4% of the data are selected.

Under what circumstances will the index fail?

(1) if you evaluate a column or use a function, the index of the column will be invalid

(2) mismatch of data types will cause index failure.

(3) if IS NULL or IS NOT NULL is used in the where statement, the index will fail.

(4) if a reverse operation is used, the index will not work

(5) if link operation is used, the index will not work.

(6) when using OR in WHERE, one column does not have an index, then the indexes of other columns will not work.

The above is all the contents of the article "when do you need to use an index in a MySQL database?" Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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