(mysql.info) identifier-qualifiers

(mysql.info) name-case-sensitivity
 
 9.2.1 Identifier Qualifiers
 ---------------------------
 
 MySQL allows names that consist of a single identifier or multiple
 identifiers. The components of a multiple-part name should be separated
 by period (‘`.'’) characters. The initial parts of a multiple-part
 name act as qualifiers that affect the context within which the final
 identifier is interpreted.
 
 In MySQL you can refer to a column using any of the following forms:
 
 *Column Reference*     *Meaning*
 COL_NAME               The column COL_NAME from whichever table used in
                        the statement contains a column of that name.
 TBL_NAME.COL_NAME      The column COL_NAME from table TBL_NAME of the
                        default database.
 DB_NAME.TBL_NAME.COL_NAMEThe column COL_NAME from table TBL_NAME of the
                        database DB_NAME.
 
 If any components of a multiple-part name require quoting, quote them
 individually rather than quoting the name as a whole. For example,
 ``my-table`.`my-column`' is legal, whereas ``my-table.my-column`' is
 not.
 
 You need not specify a TBL_NAME or DB_NAME.TBL_NAME prefix for a column
 reference in a statement unless the reference would be ambiguous.
 Suppose that tables `t1' and `t2' each contain a column `c', and you
 retrieve `c' in a `SELECT' statement that uses both `t1' and `t2'. In
 this case, `c' is ambiguous because it is not unique among the tables
 used in the statement. You must qualify it with a table name as `t1.c'
 or `t2.c' to indicate which table you mean. Similarly, to retrieve from
 a table `t' in database `db1' and from a table `t' in database `db2' in
 the same statement, you must refer to columns in those tables as
 `db1.t.col_name' and `db2.t.col_name'.
 
 A word that follows a period in a qualified name must be an identifier,
 so it is not necessary to quote it, even if it is a reserved word.
 
 The syntax .TBL_NAME means the table TBL_NAME in the default database.
 This syntax is accepted for ODBC compatibility because some ODBC
 programs prefix table names with a ‘`.'’ character.
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