Shulou(Shulou.com)06/01 Report--

In this issue, the editor will bring you a detailed explanation of the concepts of Using where and Using index in MySQL query optimization. The article is rich in content and analyzes and describes it from a professional point of view. I hope you can get something after reading this article.

"Using where; Using index" often appears in the Extra column in MySQL's query execution plan.

The official MySQL manual explains:

Using index does not read data files and only gets data from index files

Using where filter tuples have nothing to do with whether to read data files or index files

But the MySQL manual says at Using index:

1 there is no Using where, only Using index: do not read the data file, all fields can be obtained from the index (Without Using where, the optimizer may be reading the index to avoid reading data rows but not using it for lookups)

2 has both Using where and Using index: because "Without Using where..." This context means that if you have both Using where and Using index, you must read the data file.

Using where only filters tuples and has nothing to do with reading data files or index files.

The above is the detailed explanation of the concepts of Using where and Using index in MySQL query optimization shared by the editor. If you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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