TO_CLOB

TO_CLOB(lob_column | char)

-- Create a new table named tbl_nclob
CREATE TABLE tbl_nclob (
    -- Add a column named COL1 with the NUMBER data type and a maximum precision of 38
    COL1 NUMBER(38),

    -- Add a column named COL_CHAR with the VARCHAR2 data type and a maximum length of 100 characters
    COL_CHAR VARCHAR2(100),

    -- Add a column named COL_CLOB with the CLOB data type for storing large text data
    COL_CLOB CLOB
);

obclient> DESC tbl_nclob;
+----------+---------------+------+-----+---------+-------+
| FIELD    | TYPE          | NULL | KEY | DEFAULT | EXTRA |
+----------+---------------+------+-----+---------+-------+
| COL1     | NUMBER(38)    | YES  | NULL | NULL    | NULL  |
| COL_CHAR | VARCHAR2(100) | YES  | NULL | NULL    | NULL  |
| COL_CLOB | CLOB          | YES  | NULL | NULL    | NULL  |
+----------+---------------+------+-----+---------+-------+
3 rows in set

obclient> UPDATE tbl_nclob SET col_clob = TO_CLOB (col_char);
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0