In Oracle, the EMPTY_CLOB function creates an empty CLOB locator i.e. an empty (with 0 length), but non-NULL CLOB value.
In MySQL, you can use '' constant (empty string).
Oracle:
-- A sample table CREATE TABLE t1 ( c1 CLOB DEFAULT EMPTY_CLOB() );
MySQL:
-- A sample table CREATE TABLE t1 ( c1 LONGTEXT DEFAULT ('') ); /* Query OK, 0 rows affected */
Note that for a CLOB 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.