Oracle 1z0-071 Exam With Confidence Using Practice Dumps

Unused columns are a feature in Oracle that allows a column to be marked as unused without immediately dropping it from the table structure. The key points for each option are:

A. The DESCRIBE command does not display unused columns. These columns are also not visible in user_tab_cols but are visible in user_unused_col_tabs.

B. Primary key columns can be set to unused, but you must drop the primary key constraint before doing so.

C. Once a column is marked as unused, it is not possible to query it, and Oracle will not allow DML operations on that column.

D. This is true. Once a column is set to unused, you can add a new column with the same name because Oracle essentially considers the unused column as removed from the table.

E. Just like primary key columns, a foreign key column can be marked as unused, but you must drop the foreign key constraint first.

F. This is true. Unused columns retain their data until the column is dropped using the DROP UNUSED COLUMNS command.

References:

Oracle Database SQL Language Reference, 12c Release 1 (12.1): "ALTER TABLE"

Oracle Database Administrator’s Guide, 12c Release 1 (12.1)

In Oracle Database 12c, the operations related to dropping columns from a table include several behaviors, each specified clearly in Oracle documentation and best practices:

B. A column drop is implicitly committed: Dropping a column in Oracle using the ALTER TABLE ... DROP COLUMN command is a DDL (Data Definition Language) operation, which means it cannot be rolled back. DDL commands in Oracle are automatically and implicitly committed, meaning that once a column is dropped, the action is finalized immediately.

C. A column that is referenced by another column in any other table cannot be dropped: In Oracle, if a column is being referenced by a foreign key constraint or any dependency from another table, you cannot directly drop it until those references are removed or disabled. This ensures data integrity across related tables.

E. A primary key column cannot be dropped: The primary key constraint is critical for identifying unique rows within a table. Oracle does not allow the dropping of columns that are part of a primary key without first dropping the constraint or modifying it to exclude the column you intend to drop.

References:

Oracle Database SQL Language Reference 12c, specifically sections discussing DDL operations and constraints.

In Oracle Database 12c, the operations related to dropping columns from a table include several behaviors, each specified clearly in Oracle documentation and best practices:

B. A column drop is implicitly committed: Dropping a column in Oracle using the ALTER TABLE ... DROP COLUMN command is a DDL (Data Definition Language) operation, which means it cannot be rolled back. DDL commands in Oracle are automatically and implicitly committed, meaning that once a column is dropped, the action is finalized immediately.

C. A column that is referenced by another column in any other table cannot be dropped: In Oracle, if a column is being referenced by a foreign key constraint or any dependency from another table, you cannot directly drop it until those references are removed or disabled. This ensures data integrity across related tables.

E. A primary key column cannot be dropped: The primary key constraint is critical for identifying unique rows within a table. Oracle does not allow the dropping of columns that are part of a primary key without first dropping the constraint or modifying it to exclude the column you intend to drop.

References:

Oracle Database SQL Language Reference 12c, specifically sections discussing DDL operations and constraints.

Based on the given PRODUCTS table and the SQL queries provided:

Query 1: Excludes rows where prod_list is 10 or 20 and category_id is 1.

Query 2: Includes rows where prod_list is neither 10 nor 20 and category_id is 1.

Query 3: Excludes rows where prod_list is both 10 and 20 (which is not possible for a single value) and category_id is 1.

The correct answer is A, queries 1 and 3 will produce the same result. Both queries exclude rows where prod_list is 10 or 20 and include only rows from category_id 1. The NOT IN operator excludes the values within the list, and <> ALL operator ensures that prod_list is not equal to any of the values in the list, which effectively excludes the same set of rows.

Query 2, using the <> ANY operator, is incorrect because this operator will return true if prod_list is different from any of the values in the list, which is not the logic represented by the other two queries.