As far as my personal habit is concerned, I start by looking at the row with the most rows, then look at the type row, first solve the problem of type=ALL, and then look at the Extra column to see what needs to be optimized. If you don’t understand, first Baidu what these parameters mean, and then think about the optimization problem, row means how many rows are queried in the table under the table column corresponding to the row, and then type=ALL means that the row corresponds to the table column. The table below uses a full table scan. There are some others that are too long to talk about, so just Baidu them yourself.
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The poster can refer to this very detailed http://www.cnitblog.com/aliyi...
As far as my personal habit is concerned, I start by looking at the row with the most rows, then look at the type row, first solve the problem of type=ALL, and then look at the Extra column to see what needs to be optimized. If you don’t understand, first Baidu what these parameters mean, and then think about the optimization problem, row means how many rows are queried in the table under the table column corresponding to the row, and then type=ALL means that the row corresponds to the table column. The table below uses a full table scan. There are some others that are too long to talk about, so just Baidu them yourself.