MySQL - Error 1045 - Access Denied

MySQL ERROR 1045 (28000): Access denied for user 'bill'@'localhost' (using password: YES)

You probably have an anonymous user ''@'localhost' or ''@'127.0.0.1'.

As per the manual:

When multiple matches are possible, the server must determine which of
them to use. It resolves this issue as follows: (...)

When a client attempts to connect, the server looks through the rows [of table mysql.user] in sorted order.

The server uses the first row that matches the client host name and user name.

(...)
The server uses sorting rules that order rows with the most-specific Host values first.
Literal host names [such as 'localhost'] and IP addresses are the most specific.

Hence, such an anonymous user would "mask" any other user like '[any_username]'@'%' when connecting from localhost.

'bill'@'localhost' does match 'bill'@'%', but would match (e.g.) ''@'localhost' beforehands.

The recommended solution is to drop this anonymous user (this is usually a good thing to do anyways).

Below edits are mostly irrelevant to the main question. These are only meant to answer some questions raised in other comments within this thread.

Edit 1

Authenticating as 'bill'@'%' through a socket.



    root@myhost:/home/mysql-5.5.16-linux2.6-x86_64# ./mysql -ubill -ppass --socket=/tmp/mysql-5.5.sock
    Welcome to the MySQL monitor (...)

    mysql> SELECT user, host FROM mysql.user;
    +------+-----------+
    | user | host      |
    +------+-----------+
    | bill | %         |
    | root | 127.0.0.1 |
    | root | ::1       |
    | root | localhost |
    +------+-----------+
    4 rows in set (0.00 sec)

    mysql> SELECT USER(), CURRENT_USER();
    +----------------+----------------+
    | USER()         | CURRENT_USER() |
    +----------------+----------------+
    | bill@localhost | bill@%         |
    +----------------+----------------+
    1 row in set (0.02 sec)

    mysql> SHOW VARIABLES LIKE 'skip_networking';
    +-----------------+-------+
    | Variable_name   | Value |
    +-----------------+-------+
    | skip_networking | ON    |
    +-----------------+-------+
    1 row in set (0.00 sec)

Edit 2

Exact same setup, except I re-activated networking, and I now create an anonymous user ''@'localhost'.



    root@myhost:/home/mysql-5.5.16-linux2.6-x86_64# ./mysql
    Welcome to the MySQL monitor (...)

    mysql> CREATE USER ''@'localhost' IDENTIFIED BY 'anotherpass';
    Query OK, 0 rows affected (0.00 sec)

    mysql> Bye

    root@myhost:/home/mysql-5.5.16-linux2.6-x86_64# ./mysql -ubill -ppass \
        --socket=/tmp/mysql-5.5.sock
    ERROR 1045 (28000): Access denied for user 'bill'@'localhost' (using password: YES)
    root@myhost:/home/mysql-5.5.16-linux2.6-x86_64# ./mysql -ubill -ppass \
        -h127.0.0.1 --protocol=TCP
    ERROR 1045 (28000): Access denied for user 'bill'@'localhost' (using password: YES)
    root@myhost:/home/mysql-5.5.16-linux2.6-x86_64# ./mysql -ubill -ppass \
        -hlocalhost --protocol=TCP
    ERROR 1045 (28000): Access denied for user 'bill'@'localhost' (using password: YES)

Edit 3

Same situation as in edit 2, now providing the anonymous user's password.



    root@myhost:/home/mysql-5.5.16-linux2.6-x86_64# ./mysql -ubill -panotherpass -hlocalhost
    Welcome to the MySQL monitor (...)

    mysql> SELECT USER(), CURRENT_USER();
    +----------------+----------------+
    | USER()         | CURRENT_USER() |
    +----------------+----------------+
    | bill@localhost | @localhost     |
    +----------------+----------------+
    1 row in set (0.01 sec)

Conclusion 1, from edit 1: One can authenticate as 'bill'@'%'through a socket.

Conclusion 2, from edit 2: Whether one connects through TCP or through a socket has no impact on the authentication process (except one cannot connect as anyone else but 'something'@'localhost' through a socket, obviously).

Conclusion 3, from edit 3: Although I specified -ubill, I have been granted access as an anonymous user. This is because of the "sorting rules" advised above. Notice that in most default installations, a no-password, anonymous user exists (and should be secured/removed).

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)

Note: For MySQL 5.7+, please see the answer from Lahiru to this question. That contains more current information.

For MySQL < 5.7:

The default root password is blank (i.e., an empty string), not root. So you can just log in as:

mysql -u root

You should obviously change your root password after installation:

mysqladmin -u root password [newpassword]

In most cases you should also set up individual user accounts before working extensively with the database as well.

ERROR 1045 (28000): Access denied for user 'root'@'localhost'

I got the answer myself. Seemingly, if you get this error, it means that you need to reset your password. You can learn how to do that in MySQL from this link.

And don't forget to change the 5.7 version with your currently installed version in using commands (mine was 8.0).
After that, everything was working fine for me.

MySql ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

Just to confirm: You are sure you are running MySQL 5.7, and not MySQL 5.6 or earlier version. And the plugin column contains "mysql_native_password". (Before MySQL 5.7, the password hash was stored in a column named password. Starting in MySQL 5.7, the password column is removed, and the password has is stored in the authentication_string column.) And you've also verified the contents of authentication string matches the return from PASSWORD('mysecret'). Also, is there a reason we are using DML against the mysql.user table instead of using the SET PASSWORD FOR syntax?
– spencer7593

So Basically Just make sure that the Plugin Column contains "mysql_native_password".

Not my work but I read comments and noticed that this was stated as the answer but was not posted as a possible answer yet.