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Notice: Undefined index: HTTPS in /www/wwwroot/mengmianren.com/wp-content/plugins/dessky-cache/dessky-cache.php on line 43 :允许空值的字段上可以定义主键约束A、允许空值的字段上不能定义主键约束B、可以将包含多个字段的字段组合设置为主键C、一个表中只能设置一个主键约束D、允许空值的字段上可以定义主键约束正确 – 萌面人博客