After the php value is transferred, the database cannot be found.

After passing the php value, you cannot find the database and create a simple student management system & nbsp; & lt;/select & gt; & nbsp; & nbsp; major: & lt; select & nbsp; name = "pro" & gt; & nbsp; the database cannot be found after the & nbsp php value is passed
A simple student management system
Major:
Computer Science and Technology
Network Engineering
Financial Management
All
Options above
Here is the database search
If ($ pro! = "All ")
{
$ Query = "select * from s where pro = $ pro ";
}
Why can't I find a matching value in the database?
The system prompts that query is null.
This data already exists in the database
------ Solution --------------------
At least.
$ Query = "select * from s where pro = '$ Pro '";