在ubuntu中安装好spyder后, 打开spyder发现无法输入. 在打开spyder的终端窗口,有如下提示: QXcbConnection: Failed to initialize XRandr Qt: XKEYBOARD extension not present on the X server. Qt: Could not determine keyboard configuration data from X server, will use hard-coded keymap c
在openvpn 的服务器配置文件添加配置设置客户端连接后自动添加一条路由 示例: vim /etc/openvpn/server.conf # Push routes to the client to allow it # to reach other private subnets behind # the server. Remember that these # private subnets will also need # to know to route the OpenVPN c
从多表连接后的select count(*)看待SQL优化 一朋友问我,以下这SQL能直接改写成select count(*) from a吗? SELECT COUNT(*) FROM a LEFT JOIN b ON a.a1 = b.b1 LEFT JOIN c ON b.b1 = c.c1 废话不多说,直接上实验. 1. 准备数据 创建测试表a,b,c,并插入数据,a有重复数据,b是唯一数据,c是唯一数据,d有重复数据. 1) 创建a表 create table a (a1 int);