{EXPLAIN | DESCRIBE | DESC}
tbl_name [col_name | wild]

{EXPLAIN | DESCRIBE | DESC}
    [explain_type]
    {explainable_stmt | FOR CONNECTION connection_id}

{EXPLAIN | DESCRIBE | DESC} ANALYZE [FORMAT = TREE] select_statement
explain_type: {
    FORMAT = format_name
}
format_name: {
    TRADITIONAL
  | JSON
  | TREE
}
explainable_stmt: {
    SELECT statement
  | TABLE statement
  | DELETE statement
  | INSERT statement
  | REPLACE statement
  | UPDATE statement
}

DESCRIBE provides information about the columns in a table:DESCRIBE提供有关表中列的信息：

mysql> DESCRIBE City;
+------------+----------+------+-----+---------+----------------+
| Field      | Type     | Null | Key | Default | Extra          |
+------------+----------+------+-----+---------+----------------+
| Id         | int(11)  | NO   | PRI | NULL    | auto_increment |
| Name       | char(35) | NO   |     |         |                |
| Country    | char(3)  | NO   | UNI |         |                |
| District   | char(20) | YES  | MUL |         |                |
| Population | int(11)  | NO   |     | 0       |                |
+------------+----------+------+-----+---------+----------------+

DESCRIBE is a shortcut for SHOW COLUMNS. DESCRIBE是SHOW COLUMNS的快捷方式。These statements also display information for views. 这些语句还显示视图的信息。The description for SHOW COLUMNS provides more information about the output columns. SHOW COLUMNS的说明提供了有关输出列的更多信息。See Section 13.7.7.5, “SHOW COLUMNS Statement”.请参阅第13.7.7.5节，“SHOW COLUMNS语句”。

By default, DESCRIBE displays information about all columns in the table. 默认情况下，DESCRIBE显示有关表中所有列的信息。col_name, if given, is the name of a column in the table. col_name（如果给定）是表中一列的名称。In this case, the statement displays information only for the named column. 在本例中，该语句仅显示命名列的信息。wild, if given, is a pattern string. 如果给定wild，则为模式字符串。It can contain the SQL % and _ wildcard characters. 它可以包含SQL%和_通配符。In this case, the statement displays output only for the columns with names matching the string. 在本例中，语句仅显示名称与字符串匹配的列的输出。There is no need to enclose the string within quotation marks unless it contains spaces or other special characters.除非字符串包含空格或其他特殊字符，否则不需要将字符串括在引号内。

The DESCRIBE statement is provided for compatibility with Oracle.提供DESCRIBE语句是为了与Oracle兼容。

The SHOW CREATE TABLE, SHOW TABLE STATUS, and SHOW INDEX statements also provide information about tables. SHOW CREATE TABLE、SHOW TABLE STATUS和SHOW INDEX语句还提供有关表的信息。See Section 13.7.7, “SHOW Statements”.请参阅第13.7.7节，“SHOW语句”。

The EXPLAIN statement provides information about how MySQL executes statements:EXPLAIN语句提供有关MySQL如何执行语句的信息：

EXPLAIN requires the same privileges required to execute the explained statement. Additionally, EXPLAIN also requires the SHOW VIEW privilege for any explained view. EXPLAIN ... FOR CONNECTION also requires the PROCESS privilege if the specified connection belongs to a different user.

With the help of EXPLAIN, you can see where you should add indexes to tables so that the statement executes faster by using indexes to find rows. 在EXPLAIN的帮助下，您可以看到应该在哪里向表添加索引，以便通过使用索引查找行，语句执行得更快。You can also use EXPLAIN to check whether the optimizer joins the tables in an optimal order. To give a hint to the optimizer to use a join order corresponding to the order in which the tables are named in a SELECT statement, begin the statement with SELECT STRAIGHT_JOIN rather than just SELECT. (See Section 13.2.10, “SELECT Statement”.)（请参阅第13.2.10节，“SELECT语句”。）

The optimizer trace may sometimes provide information complementary to that of EXPLAIN. 优化器跟踪有时可以提供与EXPLAIN补充的信息。However, the optimizer trace format and content are subject to change between versions. 但是，优化器跟踪格式和内容在版本之间可能会发生更改。For details, see MySQL Internals: Tracing the Optimizer.有关详细信息，请参阅MySQL内部：跟踪优化器。

If you have a problem with indexes not being used when you believe that they should be, run ANALYZE TABLE to update table statistics, such as cardinality of keys, that can affect the choices the optimizer makes. 如果在您认为应该使用索引时，索引没有被使用，那么运行ANALYZE TABLE来更新表统计信息，例如键的基数，这可能会影响优化器所做的选择。See Section 13.7.3.1, “ANALYZE TABLE Statement”.请参阅第13.7.3.1节，“分析表报表”。

MySQL 8.0.18 introduces EXPLAIN ANALYZE, which runs a statement and produces EXPLAIN output along with timing and additional, iterator-based, information about how the optimizer's expectations matched the actual execution. MySQL 8.0.18引入了EXPLAIN ANALYSE，它运行一条语句并生成EXPLAIN输出，以及关于优化器的期望如何与实际执行相匹配的计时和其他基于迭代器的信息。For each iterator, the following information is provided:对于每个迭代器，提供以下信息：

The query execution information is displayed using the TREE output format, in which nodes represent iterators. 查询执行信息使用TREE输出格式显示，其中节点表示迭代器。EXPLAIN ANALYZE always uses the TREE output format. In MySQL 8.0.21 and later, this can optionally be specified explicitly using FORMAT=TREE; formats other than TREE remain unsupported.

EXPLAIN ANALYZE can be used with SELECT statements, as well as with multi-table UPDATE and DELETE statements. EXPLAIN ANALYZE可用于SELECT语句，以及多表UPDATE和DELETE语句。Beginning with MySQL 8.0.19, it can also be used with TABLE statements.从MySQL 8.0.19开始，它还可以用于TABLE语句。

Beginning with MySQL 8.0.20, you can terminate this statement using KILL QUERY or CTRL-C.从MySQL 8.0.20开始，可以使用KILL QUERY或CTRL-C终止此语句。

EXPLAIN ANALYZE cannot be used with FOR CONNECTION.EXPLAIN ANALYZE不能与FOR CONNECTION一起使用。

Example output:示例输出：

mysql> EXPLAIN ANALYZE SELECT * FROM t1 JOIN t2 ON (t1.c1 = t2.c2)\G
*************************** 1. row ***************************
EXPLAIN: -> Inner hash join (t2.c2 = t1.c1)  (cost=4.70 rows=6)
(actual time=0.032..0.035 rows=6 loops=1)
    -> Table scan on t2  (cost=0.06 rows=6)
(actual time=0.003..0.005 rows=6 loops=1)
    -> Hash
        -> Table scan on t1  (cost=0.85 rows=6)
(actual time=0.018..0.022 rows=6 loops=1)

mysql> EXPLAIN ANALYZE SELECT * FROM t3 WHERE i > 8\G
*************************** 1. row ***************************
EXPLAIN: -> Filter: (t3.i > 8)  (cost=1.75 rows=5)
(actual time=0.019..0.021 rows=6 loops=1)
    -> Table scan on t3  (cost=1.75 rows=15)
(actual time=0.017..0.019 rows=15 loops=1)

mysql> EXPLAIN ANALYZE SELECT * FROM t3 WHERE pk > 17\G
*************************** 1. row ***************************
EXPLAIN: -> Filter: (t3.pk > 17)  (cost=1.26 rows=5)
(actual time=0.013..0.016 rows=5 loops=1)
    -> Index range scan on t3 using PRIMARY  (cost=1.26 rows=5)
(actual time=0.012..0.014 rows=5 loops=1)

The tables used in the example output were created by the statements shown here:示例输出中使用的表由以下语句创建：

CREATE TABLE t1 (
    c1 INTEGER DEFAULT NULL,
    c2 INTEGER DEFAULT NULL
);

CREATE TABLE t2 (
    c1 INTEGER DEFAULT NULL,
    c2 INTEGER DEFAULT NULL
);

CREATE TABLE t3 (
    pk INTEGER NOT NULL PRIMARY KEY,
    i INTEGER DEFAULT NULL
);

Values shown for actual time in the output of this statement are expressed in milliseconds.此语句输出中显示的actual time值以毫秒为单位。