Sometimes during development of new
systems, you may add new columns to tables and then you don't use it and forget
dropping it.
So you want to know which these columns to
drop.
Usually unused columns have NULL value, So
I created a function to return array of column names in my schema have NULL
value.
I created GET_NULL_COLUMNS function
returns VARRAY of varchar2
It has only one parameter (IN_TABLE_NAME)
If I pass a value for IN_TABLE_NAME then
it will return NULL columns in this table only, otherwise it will return NULL
columns in entire schema.
CREATE OR REPLACE FUNCTION GET_NULL_COLUMNS
(
IN_TABLE_NAME VARCHAR2 DEFAULT NULL)
RETURN SYS.ODCIVARCHAR2LIST
IS
L_NULL_COLS SYS.ODCIVARCHAR2LIST
:= SYS.ODCIVARCHAR2LIST ();
LN$ROW_COUNT NUMBER;
LN$NULL_COUNT NUMBER;
LN$INDEX NUMBER := 1;
CURSOR LCUR$COLS (P_TABLE_NAME VARCHAR2)
IS
SELECT TABLE_NAME, COLUMN_NAME
FROM USER_TAB_COLS
WHERE DECODE (P_TABLE_NAME, TABLE_NAME, 1, NULL, 1, 0) = 1;
BEGIN
FOR LREC$COLS IN LCUR$COLS (IN_TABLE_NAME)
LOOP
EXECUTE IMMEDIATE 'SELECT COUNT(1) FROM ' || LREC$COLS.TABLE_NAME
INTO LN$ROW_COUNT;
EXECUTE IMMEDIATE 'SELECT
COUNT(1) FROM '
|| LREC$COLS.TABLE_NAME
|| ' WHERE '
|| LREC$COLS.COLUMN_NAME
|| ' IS NULL'
INTO LN$NULL_COUNT;
IF LN$ROW_COUNT = LN$NULL_COUNT
L_NULL_COLS.EXTEND;
L_NULL_COLS (LN$INDEX) :=
LREC$COLS.TABLE_NAME || '.' || LREC$COLS.COLUMN_NAME;
LN$INDEX := LN$INDEX + 1;
END IF;
END LOOP;
RETURN L_NULL_COLS;
END;
Let's now test this function in SCOTT
schema
SELECT COLUMN_VALUE FROM TABLE
(GET_NULL_COLUMNS);
