Oracle 11g Release 2

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CREATE TABLE TABLE_1(KEY_1, FIELD_N, SOME_OTHER_FIELD, YADDA_YADDA) AS
  SELECT 123, 'ABC', 1, 1 FROM DUAL UNION ALL
  SELECT 456, 'PQR', 1, 2 FROM DUAL UNION ALL
  SELECT 456, 'PQR', 2, 4 FROM DUAL UNION ALL
  SELECT 456, 'PQR', 3, 6 FROM DUAL UNION ALL
  SELECT 456, 'PQR', 4, 8 FROM DUAL UNION ALL
  SELECT 999, 'MNO', 9, 9 FROM DUAL
6 rows affected

SELECT * FROM TABLE_1


KEY_1
FIELD_N
SOME_OTHER_FIELD
YADDA_YADDA


123
ABC
1
1

456
PQR
1
2

456
PQR
2
4

456
PQR
3
6

456
PQR
4
8

999
MNO
9
9


CREATE OR REPLACE VIEW VIEW_1 AS
  SELECT *
    FROM TABLE_1
SELECT *
  FROM VIEW_1


KEY_1
FIELD_N
SOME_OTHER_FIELD
YADDA_YADDA


123
ABC
1
1

456
PQR
1
2

456
PQR
2
4

456
PQR
3
6

456
PQR
4
8

999
MNO
9
9


UPDATE VIEW_1
  SET FIELD_N = 'XYZ'
  WHERE KEY_1 = 123
1 rows affected

SELECT *
  FROM TABLE_1


KEY_1
FIELD_N
SOME_OTHER_FIELD
YADDA_YADDA


123
XYZ
1
1

456
PQR
1
2

456
PQR
2
4

456
PQR
3
6

456
PQR
4
8

999
MNO
9
9


CREATE OR REPLACE VIEW VIEW_2 AS
  SELECT KEY_1,
         FIELD_N,
         SUM(SOME_OTHER_FIELD) AS OTHER_SUM,
         MIN(YADDA_YADDA) AS MIN_YADDA
    FROM TABLE_1
    GROUP BY KEY_1,
             FIELD_N
SELECT *
  FROM VIEW_2


KEY_1
FIELD_N
OTHER_SUM
MIN_YADDA


456
PQR
10
2

999
MNO
9
9

123
XYZ
1
1


UPDATE VIEW_2  -- will fail
  SET FIELD_N = 'TTT'
  WHERE KEY_1 = 999
ORA-01732: data manipulation operation not legal on this view