For all the RDBMS, Database Statistics are playing the main role to generate an accurate Query Execution Plan.
A Database Administrator is also very much responsible to make sure that Database Statistics is updated.

MySQL query optimizer is also preparing Query Execution Plan with the help of Statistics Information.
The auto-update Statistics configuration is also very important to keep Statistics updated.

How to enable auto-update Statistics for InnoDB engine?

We can configure innodb_stats_on_metadata variable to enable auto-update Statistics.

When this variable is enabled InnoDB updates statistics when metadata statements such as SHOW TABLE STATUS or SHOW INDEX are run, or when accessing the INFORMATION_SCHEMA.TABLES or INFORMATION_SCHEMA.STATISTICS tables.

Check innodb_stats_on_metadata is ON or OFF:

SHOW VARIABLES LIKE 'innodb_stats_on_metadata';

If innodb_stats_on_metadata is OFF, make it ON:

SET GLOBAL innodb_stats_on_metadata=ON;

When you perform command like SHOW INDEX, Statisitcs will be update.
Accuracy of statistics is depends on MySQL Server Load.

SHOW INDEXES FROM SchemaName.TableName;

You can use below query to check the Index Statistics:

SELECT 
    Table_Schema
    ,Table_Name
    ,Non_Unique
    ,Index_Schema
    ,Seq_In_Index
    ,Column_Name
    ,Collation
    ,Cardinality
    ,Index_Type
FROM information_schema.statistics 
WHERE TABLE_SCHEMA='SchemaName';

In this post, I am sharing a script to find the Index Usage Statistics of MySQL.
This is a handy script for DBAs for finding the usage of indexes, and they can also take a decision to remove the unused indexes from the database server.

Below are two different scripts:

First, using SHOW INDEX:

SHOW INDEX FROM TableName FROM DatabaseName

Second, using INFORMATION_SCHEMA.STATISTICS table:

SELECT 
    TABLE_NAME
    ,INDEX_NAME
    ,SEQ_IN_INDEX
    ,COLUMN_NAME
    ,CARDINALITY
    ,INDEX_TYPE    
FROM INFORMATION_SCHEMA.STATISTICS 
WHERE table_schema = 'DatabaseName'

You can take a decision basis on the SEQ_IN_INDEX column data.