Clarify wildcards in dbname of GRANT command.

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The wildcard characters @samp{%} and @samp{_} can be used in the @code{Host}

and @code{Db} fields of either table.

and @code{Db} fields of either table. If you wish to use for instance a

@samp{_} character as part of a database name, specify it as @samp{\_} in

the @code{GRANT} command.

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A @code{'%'} @code{Host} value in the @code{db} table means ``any host.'' A

that database.  (@strong{Warning}: if you specify @code{ON *} and you

@strong{don't} have a current database, you will affect the global privileges!)

@strong{Please note}: the @samp{_} and @samp{%} wildcards are allowed when

specifying database names in @code{GRANT} commands. This means that if you

wish to use for instance a @samp{_} character as part of a database name,

you should specify it as @samp{\_} in the @code{GRANT} command, to prevent

the user from being able to access additional databases matching the

wildcard pattern, e.g., @code{GRANT ... ON `foo\_bar`.* TO ...}.

In order to accommodate granting rights to users from arbitrary hosts,

MySQL supports specifying the @code{user_name} value in the form

@code{user@@host}.  If you want to specify a @code{user} string

can quote the user or host name (for example, @code{'test-user'@@'test-hostname'}).

You can specify wildcards in the hostname.  For example,

@code{user@@"%.loc.gov"} applies to @code{user} for any host in the

@code{loc.gov} domain, and @code{user@@"144.155.166.%"} applies to @code{user}

@code{user@@'%.loc.gov'} applies to @code{user} for any host in the

@code{loc.gov} domain, and @code{user@@'144.155.166.%'} applies to @code{user}

for any host in the @code{144.155.166} class C subnet.

The simple form @code{user} is a synonym for @code{user@@"%"}.