Oracle SQL: the Essential Reference

TO_LOB

TO_LOB(long_column)

Converts a LONG or LONG RAW value into a CLOB, BLOB, or NCLOB. This function can be used only in the subquery of an INSERT . . . SELECT FROM statement when using that statement to populate a LOB column. LONG values are converted to either CLOB or NCLOB values, depending on the destination column's datatype. LONG RAW values are converted to BLOB values.

Example

SQL> CREATE TABLE lob_table(x CLOB);

Table created.

SQL> CREATE TABLE long_table(x LONG);

Table created.

SQL> INSERT INTO long_table (x) VALUES ('test');

1 row created.

SQL> INSERT INTO lob_table (x)
  2     SELECT TO_LOB(x)
  3     FROM long_table;

1 row created.