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• Table 

The name of the table. 

• Non_unique 

0 if the index cannot contain duplicates, 1 if it can. 

• Key_name 

The name of the index. If the index is the primary key, the name is always PRIMARY . 

• Seq_in_index 

The column sequence number in the index, starting with 1. 

• Column_name 

The column name. See also the description for the Expression  column. 

• Collation 

How the column is sorted in the index. This can have values A  (ascending), D  (descending), or NULL  (not sorted). 

• Cardinality 

An estimate of the number of unique values in the index. To update this number, run ANALYZE TABLE or (for MyISAM  tables) myisamchk -a . 

Cardinality  is counted based on statistics stored as integers, so the value is not necessarily exact even for small tables. The higher the cardinality, the greater the chance that MySQL uses the index when doing joins. 

• Sub_part 

The index prefix. That is, the number of indexed characters if the column is only partly indexed, NULL  if the entire column is indexed. 

<img src='content_image/681563.jpg'>

## Note 

Prefix limits  are measured in bytes. However, prefix lengths  for index specifications in CREATE TABLE , ALTER TABLE , and CREATE INDEX statements are interpreted as number of characters for nonbinary string types ( CHAR , VARCHAR , TEXT ) and number of bytes for binary string types ( BINARY , VARBINARY , BLOB ). Take this into account when specifying a prefix length for a nonbinary string column that uses a multibyte character set. 

For additional information about index prefixes, see Section 8.3.5, “Column Indexes” , and Section 13.1.15, “CREATE INDEX Statement” . 

• Packed 

Indicates how the key is packed. NULL  if it is not. 

• Null 

Contains YES  if the column may contain NULL  values and ’’  if not. 

