DMBS：与PhpMyAdmin和MySql opninons的并集，交集和差异

Question

I'm learning SQL and some friend adviced me to instal XAMPP as it's all preconfigured and ready to use. Well, I installed it and now I created 2 databases on which I exercise through PhpMyAdmin. That said, I'm trying to do 2 things:

a)Sets OperationsUnion, Intersect, Difference. The only available in PhpMyAdmin (and therefore MySql I guess, since I noticed that PhpMyAdmin is based on MySql) is UNION. INTERSECT AND DIFFERENCE keywords do not exist. How to do that then?

b)Using directly mysql.exe console. I try to use commands like USE databasename and so on, but it says "Access denied to user ''@'localhost to 'databasename'

I tried to put connect commands in all the flavours possible (connect user pass host db, connect user pass db, and all kind of combinations) but with no avail.

How to do that? Seems like Phpmyadmin set his own passwords for the databases. I put empty password and checked in the Phpmyadmin that those password were empty passwords. What I am doing wrong?

Answer 1

UNION keyword work perfectly fine on phpmyadmin. Phpmyadmin is just an interface for MySQL. Try to use "SQL" view in phpmyadmin to directly test your SQL queries.

If it comes to mysql.exe, try to connect using a user eg root@localhost . By default there should be no password for root.

Answer 2

a) UNION is a MySQL keyword that is a union of two queries. This is different than the union , intersection , and difference concepts , which are all achieved through JOIN s. This may help explain

b) As for your password, the username probably defaults to root , but it could be something else. If you didn't set it up, the password is probably empty string. Maybe try running xampp\\mysql\\resetroot.bat