Which three statements are true about dropping and unused columns in an Oracle database? (Choose three.)
Which three statements are true about dropping and unused columns in an Oracle database? (Choose three.)
A primary key column referenced by another column as a foreign key can be dropped if using the CASCADE option. Partition key columns cannot be dropped in Oracle databases, as attempting to do so will result in an error. A column that is set to UNUSED still counts towards the limit of 1000 columns per table.
• Answer A is RIGHT: Oders is Parent table with PRIMARY KEY ord_no, Order_items is child table which ord_no is REFERENCE KEY that reference ord_no of Parent table, now drop PRIMARY KEY on Orders by command: ALTER TABLE orders DROP COLUMN ORD_NO CASCADE CONSTRAINTS; • Answer D is RIGHT: ORA-12984: cannot drop partitioning column • Answer F is RIGHT: Unused Columns Count against 1000-column Table Limit Causing ORA-01792 on Compressed Table (Doc ID 2259600.1) and "ORA-01792: Maximum Number Of Columns In A Table Or View Is 1000" AND HIDDEN_COLUMN name is recreated with date and timestamp (Doc ID 2624150.1)
i agree
It should be A, D and F.
i think so too F is true - i tested it BC are false A is true, but you have to add it to ALTER TABLE <table_mame> SET unused (<column_name>) CASCADE CONSTRAINTS; before you drop unused constraints E should be wrong, could not find a way to undo this with roll back, this seems already the case if it is set to unused
Is B really correct? According to: https://docs.oracle.com/en/database/oracle/oracle-database/19/admin/managing-tables.html#GUID-29CA8FDC-55FB-4BEF-AE4A-5D1B4D2BE1E1 "The ALTER TABLE...DROP UNUSED COLUMNS statement is the only action allowed on unused columns. It physically removes unused columns from the table and reclaims disk space. "
F is true Unused Columns Count against 1000-column Table Limit Causing ORA-01792 on Compressed Table (Doc ID 2259600.1)
A,D e F
A,D,F is correct
A, D and F
A and D and F
Its ADF
ADF is correct
B is not correct, once, the data remains in the table, but not available for querying.
A is correct B is correct F is correct : Unused columns count against the 1000-column limit for tables in an Oracle database. The total count of columns that count against this limit can be obtained by getting a count from DBA_TAB_COLS
D is correct, partition table will not work otherwise Same with A and F
A - TRUE; e.g. ALTER TABLE departments DROP COLUMN deptno CASCADE CONSTRAINTS; B - FALSE; In Oracle Database 19c, the space occupied by an unused column is automatically reclaimed when the row containing that column is next updated. The space is released and becomes available for reuse within the block. C - FALSE; see B D - TRUE; partition key column cannot be dropped. When an attempt to drop the column is made, an error "ORA-12984: cannot drop partitioning column" occurs. E - TRUE; ALTER TABLE documentation says "Until you actually drop these columns, they continue to count toward the absolute limit of 1000 columns in a single table."
I am sorry, last two options are E - FALSE; DDL commands cannot be rolled back F - TRUE; ALTER TABLE documentation says "Until you actually drop these columns, they continue to count toward the absolute limit of 1000 columns in a single table."
Drop column cannot be rolled back