php开启mysqli扩展的方法：首先打开php.ini配置文件；然后找到【extension=php_mysqli.dll】，并取消注释；最后找到【extension_dir】，设置ext路径即可。
具体步骤：
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首先打开php.ini配置文件，搜索php_mysqli.dll；
然后设置extension_dir指令; Windows Extensions
; Note that ODBC support is built in, so no dll is needed for it.
; Note that many DLL files are located in the extensions/ (PHP 4) ext/ (PHP 5+)
; extension folders as well as the separate PECL DLL download (PHP 5+).
; Be sure to appropriately set the extension_dir directive.
;一定要适当地设置extension_dir指令。
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最后在php.ini里面搜索extension_dir；
extension_dir = “G:/web/php7.1/ext”
检查G:/web/php7.1/ext安装路径是否存在php_mysqli.dll(如果不存在应该是PHP安装包损坏，请重新下载)。
完成以上步骤就开启成功了。
