Syntax:
CONVERT(expr USING transcoding_name)

CONVERT(expr,type)

CONVERT(expr USING transcoding_name) is standard SQL syntax. The
non-USING form of CONVERT() is ODBC syntax.

CONVERT(expr USING transcoding_name) converts data between different
character sets. In MySQL, transcoding names are the same as the
corresponding character set names. For example, this statement converts
the string 'abc' in the default character set to the corresponding
string in the utf8 character set:

SELECT CONVERT('abc' USING utf8);

CONVERT(expr, type) syntax (without USING) takes an expression and a
type value specifying a result type, and produces a result value of the
specified type. This operation may also be expressed as CAST(expr AS
type), which is equivalent. For more information, see the description
of CAST().

URL: https://dev.mysql.com/doc/refman/5.7/en/cast-functions.html

