SHOW Statements • Table • Non_unique • Key_name • Seq_in_index • Collation • Column_name • Cardinality • Sub_part • Packed • Null 2936 Contains  YES  if the column may contain  NULL  values and  ’’  if not. Indicates how the key is packed.  NULL  if it is not. For additional information about index prefixes, see Section 8.3.5, “Column Indexes” , and Section 13.1.15, “CREATE INDEX Statement” . 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. The index prefix. That is, the number of indexed characters if the column is only partly indexed,  NULL  if the entire column is indexed. 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. An estimate of the number of unique values in the index. To update this number, run  ANALYZE TABLE or (for  MyISAM  tables)  myisamchk -a . How the column is sorted in the index. This can have values  A  (ascending),  D  (descending), or  NULL  (not sorted). The column name. See also the description for the  Expression  column. The column sequence number in the index, starting with 1. The name of the index. If the index is the primary key, the name is always  PRIMARY . 0 if the index cannot contain duplicates, 1 if it can. The name of the table. Note