The first reason: the database can't connect because of the permission problem. The solution is to detect the security limit of computer, security settings and the security limit of operating system. You can temporarily turn off the firewall or antivirus software to see if it is caused by the security settings of these software.
Cause 2: Network connection failure. The solution is to check whether the network is faulty.
A database is a warehouse for storing data. Its storage space is very large, and it can store millions, tens of millions and hundreds of millions of pieces of data. But the database does not store data at will, and there are certain rules, otherwise the query efficiency will be very low. Today's world is an internet world full of data, full of a lot of data. That is, this internet world is the data world. There are many sources of data, such as travel records, consumption records, web pages visited, messages sent and so on. Besides text data, images, music and sounds are all data.