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What is the role of the EXPLAIN command in MySQL, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

The sequence number of the ID SELECT command (usually 1, and subqueries often start with the sequence number 2)

Select_type

SIMPLE simple SELECT command

The outermost SELECT command of PRIMARY

UNION SELECT commands connected by UNION statements

DEPENDENT UNION SELECT commands connected by UNION statements (dependent on external queries)

SELECT command in SUBQUERY subquery

SELECT commands in DEPENDENT SUBQUERY subqueries (dependent on external queries)

DERIVED derived tables (subqueries of FROM statements)

Table table name

Type

The connection type of the table (sorted by efficiency)

System has a table with only one record (= system table)

Const constant, with an index restricted by PRIMARY KEY/UNIQUE (the result is always 1 row)

Equivalent query made by PRIMARY KEY/UNIQUE column when eq_ref is connected

Equivalent query for ref non-UNIQUE columns

The search of [~ OR column name IS NULL] is added to ref_or_null ref.

Range uses the index to check a range of records (=, >, > =

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