UPDATE table1 SET 
    column1 = DECODE(table1.column1,null,null,'no info','no info','default value'), 
    column2 = DECODE(table1.column2,null,null,'no info','no info','another default value'), 
    column3 = 'default value'

CREATE TABLE table1_tmp PARALLEL NOLOGGING 
    AS (select col1,col2,col3,col4 from table1)

ALTER TABLE table1_tmp ADD ( col5 VARCHAR(10) default('some info') NOT NULL

ALTER TABLE table1_tmp ADD ( col6 VARCHAR(10) default('some info') NOT NULL

ALTER TABLE table1_tmp ADD ( col7 VARCHAR(10)

ALTER TABLE table1_tmp ADD ( col8 VARCHAR(10)

MERGE INTO table1_tmp tt 
    USING table1 t 
    ON (t.col1 = tt.col1) 
WHEN MATCHED THEN 
    UPDATE SET 
        tt.col7 = 'some defaul value that may be null', 
        tt.col7 = 'some value that may be null'

UPDATE table1 SET 
    column1 = DECODE(table1.column1,null,null,'no info','no info','default value'), 
    column2 = DECODE(table1.column2,null,null,'no info','no info','another default value'), 
    column3 = 'default value'

CREATE TABLE table1_tmp PARALLEL NOLOGGING 
    AS (select col1,col2,col3,col4 from table1)

ALTER TABLE table1_tmp ADD ( col5 VARCHAR(10) default('some info') NOT NULL

ALTER TABLE table1_tmp ADD ( col6 VARCHAR(10) default('some info') NOT NULL

ALTER TABLE table1_tmp ADD ( col7 VARCHAR(10)

ALTER TABLE table1_tmp ADD ( col8 VARCHAR(10)

MERGE INTO table1_tmp tt 
    USING table1 t 
    ON (t.col1 = tt.col1) 
WHEN MATCHED THEN 
    UPDATE SET 
        tt.col7 = 'some defaul value that may be null', 
        tt.col7 = 'some value that may be null'