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This article introduces you how to understand Mysql index extensions, the content is very detailed, interested friends can use for reference, hope to be helpful to you.

1. What is index extensions

The key_len of the former is 8 while that of the latter is 4, which indicates that the index that can be used is not only the iExtracc index, but also the primary key index.

The ref column value of the former is const,const, while the latter has only const, indicating that the former uses two index parts, while the latter has only one.

The rows of the former is 2, while the rows of the latter is 3, because the former is more efficient.

The latter has more Using Where in the Extra column, indicating that the latter also needs to filter the data from the results again, rather than directly using the index to get the results like the former.

We can also compare the actual execution cost of the two SQL by observing the difference in the value of Handler_read_% in STATUS (after executing FLUSH STATUS, execute the query SQL, and then execute SHOW STATUS LIKE 'Handler_read_%' to view):

The price of the latter is Handler_read_next = 3

The price of the former is Handler_read_next = 2

If the amount of data is larger, the difference will increase.

Thus it can be seen that the former is indeed more efficient than the latter.

On how to understand Mysql index extensions to share here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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