Qualifiers are used within SQL statements to reference data structures, such
as databases, tables, or columns. For example, typically a SELECT query
contains references to some columns and at least one table.

Qualifiers can be composed by one or more identifiers, where the initial parts
affect the context within which the final identifier is interpreted:

* For a database, only the database identifier needs to be specified.
* For objects which are contained in a database (like tables, views,
functions, etc) the database identifier can be specified. If no database is
specified, the current database is assumed (see USE and DATABASE() for more
details). If there is no default database and no database is specified, an
error is issued.
* For column names, the table and the database are generally obvious from the
context of the statement. It is however possible to specify the table
identifier, or the database identifier plus the table identifier.
* An identifier is fully-qualified if it contains all possible qualifiers, for
example, the following column is fully qualified: db_name.tbl_name.col_name.

If a qualifier is composed by more than one identifier, a dot (.) must be used
as a separator. All identifiers can be quoted individually. Extra spacing
(including new lines and tabs) is allowed.

All the following examples are valid:

* db_name.tbl_name.col_name
* tbl_name
* `db_name`.`tbl_name`.`col_name`
* `db_name` . `tbl_name`
* db_name. tbl_name

If a table identifier is prefixed with a dot (.), the default database is
assumed. This syntax is supported for ODBC compliance, but has no practical
effect on MariaDB. These qualifiers are equivalent:

* tbl_name
* . tbl_name
* .`tbl_name`
* . `tbl_name`

For DML statements, it is possible to specify a list of the partitions using
the PARTITION clause. See Partition Pruning and Selection for details.

URL: https://mariadb.com/kb/en/identifier-qualifiers/