Oracle 11g Release 2

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--BEGIN
--  EXECUTE IMMEDIATE 'DROP TABLE storageTable';
--END;
--/

CREATE TABLE storageTable (
  "date" NUMBER,
  "size" NUMBER
);
INSERT INTO storageTable
  SELECT
    MOD(LEVEL, 100) "date",
    TRUNC(DBMS_RANDOM.VALUE(100, 200) * 1024 * 1024) "size"
  FROM dual
  CONNECT BY LEVEL <= 1000;
1000 rows affected

  WITH t1 AS (SELECT
                ROUND(SUM("size" / 1024 / 1024)) Size_Used,
                ROW_NUMBER() OVER(ORDER BY "date" DESC) rn
              FROM storageTable
              GROUP BY "date")
  SELECT
    "1", "2", "3", "4", "5", "6", "7"
--    INTO lastRowMinus0, lastRowMinus1, lastRowMinus2, lastRowMinus3,
--         lastRowMinus4, lastRowMinus5, lastRowMinus6
  FROM (SELECT * FROM t1 WHERE rn < 8) t2
  PIVOT(SUM(Size_Used) FOR rn IN(1, 2, 3, 4, 5, 6, 7)) p;


1
2
3
4
5
6
7


1621
1514
1439
1643
1587
1469
1394


DECLARE
  lastRowMinus0 NUMBER;
  lastRowMinus1 NUMBER;
  lastRowMinus2 NUMBER;
  lastRowMinus3 NUMBER;
  lastRowMinus4 NUMBER;
  lastRowMinus5 NUMBER;
  lastRowMinus6 NUMBER;
BEGIN
  WITH t1 AS (SELECT
                ROUND(SUM("size" / 1024 / 1024)) Size_Used,
                ROW_NUMBER() OVER(ORDER BY "date" DESC) rn
              FROM storageTable
              GROUP BY "date")
  SELECT
    "1", "2", "3", "4", "5", "6", "7"
    INTO lastRowMinus0, lastRowMinus1, lastRowMinus2, lastRowMinus3,
         lastRowMinus4, lastRowMinus5, lastRowMinus6
  FROM (SELECT * FROM t1 WHERE rn < 8) t2
  PIVOT(SUM(Size_Used) FOR rn IN(1, 2, 3, 4, 5, 6, 7)) p;

  DBMS_OUTPUT.PUT_LINE('lastRowMinus0: '||lastRowMinus0||CHR(10)||
                       'lastRowMinus1: '||lastRowMinus1||CHR(10)||
                       'lastRowMinus2: '||lastRowMinus2||CHR(10)||
                       'lastRowMinus3: '||lastRowMinus3||CHR(10)||
                       'lastRowMinus4: '||lastRowMinus4||CHR(10)||
                       'lastRowMinus5: '||lastRowMinus5||CHR(10)||
                       'lastRowMinus6: '||lastRowMinus6);
END;
/
1 rows affected

dbms_output:
lastRowMinus0: 1621
lastRowMinus1: 1514
lastRowMinus2: 1439
lastRowMinus3: 1643
lastRowMinus4: 1587
lastRowMinus5: 1469
lastRowMinus6: 1394