SHOW
Syntax
1184
SHOW {INDEX | INDEXES | KEYS}
{FROM | IN}
tbl_name
[{FROM | IN}
db_name
]
[WHERE
expr
]
SHOW INDEX
returns table index information. The format resembles that of the
SQLStatistics
call in
ODBC.
SHOW INDEX
returns the following fields:
•
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.
•
Collation
How the column is sorted in the index. In MySQL, this can have values “
A
” (Ascending) or
NULL
(Not
sorted).
•
Cardinality
An estimate of the number of unique values in the index. This is updated by running
ANALYZE
TABLE
or
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 number of indexed characters if the column is only partly indexed,
NULL
if the entire column is
indexed.
•
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.
•
Index_type
The index method used (
BTREE
,
FULLTEXT
,
HASH
,
RTREE
).
•
Comment
Information about the index not described in its own column, such as
disabled
if the index is
disabled.
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