How to determine whether the index exists in mysql

In mysql, you can use the SHOW INDEX statement to determine whether the index exists. This statement can view the index created in the table. If the index exists, the result will be displayed. The syntax is "SHOW INDEX FROM table name FROM database name ".

The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.

How does mysql determine whether the index exists?

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>]

The syntax description is as follows:

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

: Specify the database where the data table whose index needs to be viewed is located, which can be omitted. For example, the SHOW INDEX FROM student FROM test; statement means to view the index of the student data table in the test database.

Example

Use the SHOW INDEX statement to view the index information of the tb_stu_info2 data table in the "MySQL Create Index" section. The SQL statement and running results are as follows.

Extended knowledge:

The main parameters are explained as follows:

• Table represents the data table to create the index Name, here is the tb_stu_info2 data table.

• Non_unique indicates 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_index indicates the position of the column in the index. If the index is a single column, the value of this column is 1; if the index is a combined index, the value of this column is 1 for each column. The order in the index definition.

• Column_name represents the column field that defines the index.

• Collation indicates 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.

• Cardinality An 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.

• Packed indicates how the keyword is 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_type displays the type and method used by the index (BTREE, FULLTEXT, HASH, RTREE).

• Comment Displays the comment.

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