1.添加PRIMARY KEY(主键索引)
ALTER TABLE `table_name` ADD PRIMARY KEY ( `column` )

2.添加UNIQUE(唯一索引)
ALTER TABLE `table_name` ADD UNIQUE (
`column`
)

3.添加INDEX(普通索引)
ALTER TABLE `table_name` ADD INDEX index_name ( `column` )

4.添加FULLTEXT(全文索引)
ALTER TABLE `table_name` ADD FULLTEXT ( `column`)

5.添加多列索引
ALTER TABLE `table_name` ADD INDEX index_name ( `column1`, `column2`, `column3` )