How to query index status in mysql?

Mysql method of querying the index status: through the "SHOW INDEX" statement, the syntax format "SHOW INDEX FROM

[ FROM ]"; through this statement, you can view the index Name, whether it is a unique index, the position of the field in the index, the column field name that defines the index, etc.

After the index creation is completed, you can use SQL statements to view the existing indexes. In MySQL, you can use the SHOW INDEX statement to view the indexes created on a table.

The syntax format for viewing the index is as follows:

SHOW INDEX FROM <表名> [ FROM <数据库名>]

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The syntax description is as follows:

• ##

: Specify the data table to be viewed for the index name.

: Specify the database where the data table whose index needs to be viewed is located, which can be omitted. For example,

SHOW INDEX FROM student FROM test; statement means to view the index of the student data table in the test database.

Example

SQL statements and running results are as follows.

mysql> SHOW INDEX FROM tb_stu_info2\G
*************************** 1. row ***************************
        Table: tb_stu_info2
   Non_unique: 0
     Key_name: height
 Seq_in_index: 1
  Column_name: height
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment:
Index_comment:
1 row in set (0.03 sec)

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The main parameters are described as follows:

ParametersDescriptionTable represents the name of the data table to create the index, here is the tb_stu_info2 data table. Non_uniqueIndicates whether the index is a unique index. If it is not a unique index, the value of this column is 1; if it is a unique index, the value of this column is 0. Key_name represents the name of the index. Seq_in_indexIndicates the position of the column in the index. If the index is a single column, the value of the column is 1; if the index is a combined index, the value of the column is 1. The column values ​​are the order in which each column appears in the index definition. Column_name represents the column field that defines the index. CollationIndicates the order in which columns are stored in the index. In MySQL, ascending order displays the value "A" (ascending order), if displayed as NULL, it means no classification. CardinalityAn estimate of the number of unique values ​​in the index. Cardinality counts against statistics that are stored as integers, so even for small tables, the value does not need to be exact. The larger the cardinality, the greater the chance that MySQL will use the index when doing joins. Sub_part represents the number of indexed characters in the column. If the column is only partially indexed, the value of the column is the number of characters indexed; if the entire column is indexed, the value of the column is NULL. PackedIndicates how keywords are packed. If not compressed, the value is NULL. Null is used to display whether the index column contains NULL. If a column contains NULL, the value of the column is YES. If not, the value of this column is NO. Index_typeDisplay the type and method used by the index (BTREE, FULLTEXT, HASH, RTREE). CommentDisplay comments. Recommended tutorial:

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