What to do if database selection fails in php

Solution to failed database selection in php: 1. Check mysql_select_db and mysqli_select_db; 2. Modify the order of incoming parameters of the two connection methods.

The operating environment of this article: Windows 7 system, PHP version 7.1, Dell G3 computer.

What should I do if the database selection fails in php?

"Failed to select database" occurs when PHP connects to the database?

When PHP connects to the database:

There is no problem connecting to the database with mysqli_connect, but there is always an error when using mysqli_select_db ! Puzzled.

After careful observation of mysql_select_db and mysqli_select_db, I found that

The incoming parameters of mysql_select_db are ($databaseName,$query);

The incoming parameters of mysqli_select_db The parameters are ($query,$databaseName);

At this point, it turns out that the order of the parameters passed in the two connection methods is not the same, so the selection failed.

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