PRIMARY KEY是唯一性索引
添加表主键
ALTER TABLE `website` ADD PRIMARY KEY (`name`);
删除&修改表主键
ALTER TABLE `website` CHANGE `id` `id` INT UNSIGNED;
ALTER TABLE `website` DROP PRIMARY KEY;
ALTER TABLE `website` ADD PRIMARY KEY (`id`);
ALTER TABLE `website` CHANGE `id` `id` INT UNSIGNED AUTO_INCREMENT;
查看索引列表
SHOW INDEX FROM `website`;
添加普通索引
CREATE INDEX `name_index` ON `website` (`name`);
添加唯一性索引（设置唯一性后，无法添加重复内容）
CREATE UNIQUE INDEX `name_index` ON `website`(`name`(80));
删除索引
DROP INDEX `name_index` ON `website`;
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