In Oracle, the EMPTY_BLOB function creates an empty BLOB locator i.e. an empty (with 0 length), but non-NULL BLOB value.
In MySQL, you can use x'' constant (empty binary string).
Oracle:
-- A sample table CREATE TABLE t1 ( c1 BLOB DEFAULT EMPTY_BLOB() );
MySQL:
-- A sample table CREATE TABLE t1 ( c1 LONGBLOB DEFAULT (x'') ); /* Query OK, 0 rows affected */
Note that for a BLOB column, you have to enclose the DEFAULT value with parentheses, otherwise you will get the error: ERROR 1101 (42000): BLOB, TEXT, GEOMETRY or JSON column can't have a default value.
For more information, see Oracle to MySQL Migration.