How to modify the index type in mysql-Mysql Tutorial-php.cn

Mysql method to modify the index type: 1. Use the "DROP INDEX index name ON table name;" statement to delete the original specified index; 2. Use "CREATE index type keyword INDEX index name ON table name (column Name [length])" statement creates an index with the same name to modify the type.

How to modify the index type in mysql

The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.

There is no direct instruction to modify the index in MySQL. Generally, we need to delete the original index first, and then create an index with the same name as needed, so as to modify the index in disguise.

mysql Modify index type

#1. Delete the original index

When the index is no longer needed , you can use the DROP INDEX statement to delete the index.

Grammar format:

DROP INDEX <索引名> ON <表名>

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The syntax description is as follows:

: The name of the index to be deleted.

: Specify the table name where the index is located.

Example:

tb_stu_info2 Index information of the data table

How to modify the index type in mysql

It can be seen from the output results : "Key_name: height"--The name of the index is "height", "Index_type: BTREE"-The type used by the index is "BTREE"

Delete the index height in the table tb_stu_info2

DROP INDEX height ON tb_stu_info2;

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2. Create an index with the same name

You can use the CREATE INDEX statement specifically used to create an index to create an index on an existing table, but this statement cannot create a primary key.

Syntax format:

CREATE <索引名> INDEX ON <表名> (<列名> [<长度>] [ ASC | DESC])

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The syntax description is as follows:

: Specify the index name. A table can create multiple indexes, but each index has a unique name in the table.

: Specify the name of the table to create an index.

: Specify the column name to create an index. You can usually consider using columns that frequently appear in the JOIN clause and WHERE clause in the query statement as index columns.

: Optional. Specifies that the length characters preceding the column are used to create the index. Creating an index using part of a column can help reduce the size of the index file and save the space occupied by the index columns. In some cases, only the prefix of a column can be indexed. The length of an index column has a maximum limit of 255 bytes (1000 bytes for MyISAM and InnoDB tables). If the length of an index column exceeds this limit, it can only be indexed using the column's prefix. In addition, columns of type BLOB or TEXT must also use prefix indexes.

ASC|DESC: Optional. ASC specifies that the index is sorted in ascending order, DESC specifies that the index is sorted in descending order, and the default is ASC.

Example:

Create a normal index

CREATE INDEX height ON tb_stu_info2 (height(8));

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When creating a unique index, the UNIQUE keyword is usually used.

CREATE UNIQUE INDEX height ON tb_stu_info2 (height(8));

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Expand knowledge:

The index types in MySQL are as follows

General Index
Unique index
Primary key index
Combined index
Full text index

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