explain value of 4

[MySQL Notes] SQL optimization tool-explain the output format of the explain command If you have experience using MySQL, you may encounter slow SQL queries in your project. In some scenarios, you can easily locate the problem (for example, when a

Transferred from: http://www.cnblogs.com/magialmoon/archive/2013/11/23/3439042.htmlMySQL official manual description of the explain naming document: Https://dev.mysql.com/doc/refman/5.7/en/explain-output.html#explain_select_typeThe recent slow

Students with MySQL experience may encounter SQL slow query scenarios in the actual project, some scenarios are easy to locate the problem (such as a single table operation with slow query SQL, carefully check SQL statements are usually easy to

Say 工欲善其事, its prerequisite. Today we will briefly introduce the next explain.Content navigation Id Select_type Table Type Possible_keys Key Key_len Ref Rows Extra Environment ready MySQL

MySQL execution Plan explain detailed 2015-08-10 13:56:27Category: MySQLThe explain command is the primary way to see how the query optimizer decides to execute a query.This feature has limitations and does not always tell the truth, but its output

How to Learn the extended option of MySQL explain statement MySQL has an explain command that can be used to analyze the running effect of the SELECT statement. For example, explain can obtain the SELECT statement.Indexes used, sorting, and

If you put the keyword explain,mysql in front of the SELECT statement, it explains how it handles the Select, providing an order about how tables are joined and joined.Each output row of the explain provides information about a table, and each row

Explain shows how MySQL uses indexes to process SELECT statements and join tables. Can help select better indexes and write more optimized query statements.Parse an SQL statement first to see what

Why is the filtered column value always 100% in Mysql explain extended?1. execute the Mysql explain extended command to output a column of filtered (MySQL5.7 outputs filtered by default ), it indicates the percentage of rows in the returned results

Mysql Explain here to do a comprehensive collation of the data. I. Grammar Explain For example: Explain select * from T3 where id=3952602; Two. Explain output interpretation +----+-------------+-------+-------+-------------------+---------+----