Syntax:
    [COLLATE 'collation_name'] | DEFAULT}

This statement sets the three session system variables
character_set_client, character_set_connection, and
character_set_results to the given character set. Setting
character_set_connection to charset_name also sets collation_connection
to the default collation for charset_name. See
http://dev.mysql.com/doc/refman/5.7/en/charset-connection.html.

The optional COLLATE clause may be used to specify a collation
explicitly. If given, the collation must one of the permitted
collations for charset_name.

The default mapping can be restored by using a value of DEFAULT. The
default depends on the server configuration.

ucs2, utf16, and utf32 cannot be used as a client character set, which
means that they do not work for SET NAMES.

URL: http://dev.mysql.com/doc/refman/5.7/en/set-names.html

