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  • MYSQL ALTER

    ALTER command to add and drop column in MySQL

    An column in MySQL can be added using ALTER statement in multiple ways as shown:

    ALTER TABLE table_name ADD column_name column_type;

    Drop:

    ALTER TABLE table_name DROP column_name;

    ALTER command to add and drop INDEX in MySQL

    Index in a database is used to improve the speed of operations in a table. Index can be done using single or multiple columns.

    There are 4 types of index commands to adding indexes to a table:

    1. ALTER TABLE tbl_name ADD PRIMARY KEY (column_list) : Adds a primary key which means adds indexes and does not allow null values.
    2. ALTER TABLE tbl_name ADD UNIQUE index_name (column_list) : Creates an index whose values must be null with the exception of NULL values.
    3. ALTER TABLE tbl_name ADD INDEX index_name (column_list) : Adds indexes in which one value can appear more than once
    4. ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list) : Adds an index for efficient text-searching purpose.



    Dropping indexes:

    To drop a primary key:

    ALTER TABLE testalter_tbl DROP PRIMARY KEY;

    To drop an index:

    DROP INDEX index_name ON tbl_name.
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  • 原文地址:https://www.cnblogs.com/maoxiaolv/p/5526472.html
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