How can I add an index in the MySQL database?

1 year ago
William Carter
1 minute

In MySQL, you can add an index using the following syntax.

  1. Add an index to the columns of an existing table.
ALTER TABLE 表名 ADD INDEX 索引名 (列名);
  1. Add a composite index on multiple columns in an existing table.
ALTER TABLE 表名 ADD INDEX 索引名 (列名1, 列名2, ...);
  1. Add a unique index to columns in an existing table.
ALTER TABLE 表名 ADD UNIQUE INDEX 索引名 (列名);
  1. Add a unique composite index on multiple columns in an already existing table.
ALTER TABLE 表名 ADD UNIQUE INDEX 索引名 (列名1, 列名2, ...);
  1. Add a full-text index to the columns of an existing table.
ALTER TABLE 表名 ADD FULLTEXT INDEX 索引名 (列名);

Please note that creating an index can be time-consuming and resource-intensive, especially for large tables. Therefore, before adding an index, make sure to backup the table structure and data, and carefully evaluate whether it is necessary to add an index to improve query performance.

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