Mysql show index解釋

<code>檢視表上的索引狀态:</code>

<code></code>

<code>SHOW INDEX</code> returns table index information.

<code>SHOW KEYS</code> and <code>SHOW INDEXES</code> are synonyms for <code>SHOW INDEX</code>.

文法:

show {index|indexes} from table_name [ from db_name ] [where expr]

The following fields are returned by <code>SHOW INDEX</code>.

Field

Description

Table

Table name

Non_unique

<code>1</code> if the index permits duplicate values, <code>0</code> if values must be unique.

Key_name

Index name. The primary key is always named <code>PRIMARY</code>.

Seq_in_index

The column's sequence in the index, beginning with <code>1</code>.

Column_name

Column name.

Collation

Either <code>A</code>, if the column is sorted in ascending order in the index, or <code>NULL</code> if it's not sorted.

Cardinality

Estimated number of unique values in the index. The cardinality statistics are calculated at various times, and can help the optimizer make improved decisions.

Sub_part

<code>NULL</code> if the entire column is included in the index, or the number of included characters if not.

Packed

<code>NULL</code> if the index is not packed, otherwise how the index is packed.

Null

<code>NULL</code> if <code>NULL</code> values are permitted in the column, an empty string if <code>NULL</code>'s are not permitted.

Index_type

Comment

Other information, such as whether the index is disabled.

Index_comment

Contents of the <code>COMMENT</code> attribute when the index was created.

本文轉自 wangergui 51CTO部落格，原文連結：http://blog.51cto.com/wangergui/2074486，如需轉載請自行聯系原作者