An identifier cannot consist entirely of digits, if it's not quoted. If the ANSI_QUOTES SQL modes is enabled, double quotes are acceptable to quote an identifier.
Database and table names can't contain '.', '/', or '\'.

For database and table identifiers, case sensitivity depends on the OS and file system of the server host, and on the setting of the lower_case_table_names system variable.
Column, index, stored routine and trigger identifiers are not case sensitive.
Column aliases are not case sensitive.

A table name may be qualified with the name of the database to which it belongs.
For example:
SELECT, FROM db1.table_a db1t_a
   INNER JOIN db2.table_b db2t_b
   ON =;