一、手动
执行Analyze table
innodb和myisam存储引擎都可以通过执行“Analyze table tablename”来收集表的统计信息，除非执行计划不准确，否则不要轻易执行该操作，如果是很大的表该操作会影响表的性能。
二、自动触发
以下行为会自动触发统计信息的收集
1.第一次打开表的时候
2.表修改的行超过1/6或者20亿条时
3.当有新的记录插入时
4.执行show index from tablename或者执行show table stauts、查询information_schema.tables\statistics 时
三、开启参数innodb_stats_on_metadata
当开启参数innodb_stats_on_metadata后访问以下表也会触发统计信息的收集
在访问以下表时，innodb表的统计信息可自动收集
information_schema.TABLES
information_schema.STATISTICS
information_schema.PARTITIONS
information_schema.KEY_COLUMN_USAGE
information_schema.TABLE_CONSTRAINTS
information_schema.REFERENTIAL_CONSTRAINTS
information_schema.table_constraints
参数说明：
Innodb_stats_sample_pages：每次收集统计信息时采样的页数，默认为20
innodb_stats_persistent：默认on，将analyze table产生的统计信息保存于磁盘，直至下次analyze table为止，此举避免了统计信息动态更新，保证了执行计划的稳定，对于大表也节省了收集统计信息的所需资源;
查询表的统计信息
mysql> select TABLE_SCHEMA,table_name,column_name,CARDINALITY from information_schema.STATISTICS b where b.table_name='salaries';
+--------------+------------+-------------+-------------+
| TABLE_SCHEMA | table_name | column_name | CARDINALITY |
+--------------+------------+-------------+-------------+
| employees | salaries | emp_no | 2843953 |
| employees | salaries | from_date | 2843953 |
+--------------+------------+-------------+-------------+
2 rows in set (0.00 sec)
mysql> show index from employees.salaries;
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| salaries | 0 | PRIMARY | 1 | emp_no | A | 2843953 | NULL | NULL | | BTREE | | |
| salaries | 0 | PRIMARY | 2 | from_date | A | 2843953 | NULL | NULL | | BTREE | | |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec) mysql> select table_rows from information_schema.tables where table_name='salaries';
+------------+
| table_rows |
+------------+
| 2843953 |
+------------+
1 row in set (0.00 sec)
mysql> select count(1) from employees.salaries;
+----------+
| count(1) |
+----------+
| 2844047 |
+----------+
1 row in set (0.52 sec)
表的真实数据为 2844047
手动分析下表在看统计信息
mysql> analyze table employees.salaries;
+--------------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+--------------------+---------+----------+----------+
| employees.salaries | analyze | status | OK |
+--------------------+---------+----------+----------+
1 row in set (0.50 sec) mysql> select table_rows from information_schema.tables where table_name='salaries';
+------------+
| table_rows |
+------------+
| 2838489 |
+------------+
1 row in set (0.01 sec) mysql> select TABLE_SCHEMA,table_name,column_name,CARDINALITY from information_schema.STATISTICS b where b.table_name='salaries';
+--------------+------------+-------------+-------------+
| TABLE_SCHEMA | table_name | column_name | CARDINALITY |
+--------------+------------+-------------+-------------+
| employees | salaries | emp_no | 2838489 |
| employees | salaries | from_date | 2838489 |
+--------------+------------+-------------+-------------+
2 rows in set (0.00 sec) mysql> show index from employees.salaries;
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| salaries | 0 | PRIMARY | 1 | emp_no | A | 2838489 | NULL | NULL | | BTREE | | |
| salaries | 0 | PRIMARY | 2 | from_date | A | 2838489 | NULL | NULL | | BTREE | | |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
统计信息和真实数据一致