Oracle 11g Release 2

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create table PRESCRIPTION_IMAGES (
  ORDER_ID NUMBER(38) NOT NULL,
  RX_IMAGE1 BLOB NOT NULL ,
  RX_IMAGE3 BLOB NOT NULL,
  RX_IMAGE4 BLOB NOT NULL,
  CREATE_DATE_TIME DATE NOT NULL,
  LAST_UPDATE_DATE_TIME DATE NOT NULL,
  RX_IMAGE2 BLOB NOT NULL
);
ALTER TABLE PRESCRIPTION_IMAGES MODIFY RX_IMAGE3 BLOB NULL;
ORA-22859: invalid modification of columns

ALTER TABLE PRESCRIPTION_IMAGES MODIFY RX_IMAGE3 NULL;
SELECT TABLE_NAME, COLUMN_NAME, DATA_TYPE, NULLABLE
FROM USER_TAB_COLUMNS
ORDER BY TABLE_NAME, COLUMN_ID;


TABLE_NAME
COLUMN_NAME
DATA_TYPE
NULLABLE


PRESCRIPTION_IMAGES
ORDER_ID
NUMBER
N

PRESCRIPTION_IMAGES
RX_IMAGE1
BLOB
N

PRESCRIPTION_IMAGES
RX_IMAGE3
BLOB
Y

PRESCRIPTION_IMAGES
RX_IMAGE4
BLOB
N

PRESCRIPTION_IMAGES
CREATE_DATE_TIME
DATE
N

PRESCRIPTION_IMAGES
LAST_UPDATE_DATE_TIME
DATE
N

PRESCRIPTION_IMAGES
RX_IMAGE2
BLOB
N

TABLE_NAME	COLUMN_NAME	DATA_TYPE	NULLABLE
PRESCRIPTION_IMAGES	ORDER_ID	NUMBER	N
PRESCRIPTION_IMAGES	RX_IMAGE1	BLOB	N
PRESCRIPTION_IMAGES	RX_IMAGE3	BLOB	Y
PRESCRIPTION_IMAGES	RX_IMAGE4	BLOB	N
PRESCRIPTION_IMAGES	CREATE_DATE_TIME	DATE	N
PRESCRIPTION_IMAGES	LAST_UPDATE_DATE_TIME	DATE	N
PRESCRIPTION_IMAGES	RX_IMAGE2	BLOB	N