Pass the Oracle PL 1z0-071 Questions and answers with ExamsMirror

To find duplicate customer details entered under different CUSTNO values, one would typically use methods that compare records within the same table:

C. Subquery: A subquery can be used to compare customer details in the CUSTOMERS table and identify duplicates. This subquery can look for matches in the customer details while having different CUSTNO.

E. Self Join: A self join can also be used for this purpose. This involves joining the CUSTOMERS table to itself on the columns containing customer details to identify rows that have the same information but different CUSTNO.

References:

Oracle Database SQL Language Reference 12c, particularly the sections on self joins and subqueries, as these can be utilized to find duplicate rows based on specified criteria.

To display unique promotion costs in each promotion category, the correct queries that can be used are:

C. SELECT DISTINCT promo_category ||' has '|| promo_cost AS COSTS FROM promotions ORDER BY 1;This query concatenates the promo_category with the literal ' has ' and promo_cost, giving a unique string for each combination of promo_category and promo_cost, which is what we are interested in when we want to list unique costs per category.

D. SELECT DISTINCT promo_category, promo_cost FROM promotions ORDER BY 1;This query selects distinct combinations of promo_category and promo_cost, which is exactly what's required to display unique promotion costs in each category.

Options A, B, and E are incorrect:

A is incorrect because it does not use the DISTINCT keyword to ensure uniqueness.

B has incorrect syntax; the DISTINCT keyword should appear directly after SELECT and applies to all columns, not just one.

E is syntactically incorrect and would not execute because the DISTINCT keyword is not used correctly. It should not appear twice in the SELECT clause.

B. CREATE INDEX price_idx on products (price); E. ALTER TABLE products DROP UNUSED COLUMNS; F. DROP TABLE products.

Comprehensive and Detailed Explanation WITH all References:

When a table is in read-only mode, most types of modifications are prohibited. However, certain operations can still be performed.

A. Incorrect. You cannot drop a column from a table that is in read-only mode, as it is a modifying operation. B. Correct. You can create an index on a read-only table. Creating an index does not modify the actual rows within the table; it builds a separate structure used for faster access. C. Incorrect. The SET UNUSED statement marks one or more columns as unused so they can be dropped when the database is not busy. This operation is considered a modifying operation and therefore is not allowed on a read-only table. D. Incorrect. Truncate is a DDL operation that would delete all rows from a table. This operation is not allowed on a read-only table. E. Correct. The ALTER TABLE ... DROP UNUSED COLUMNS statement is used to drop columns that have been previously marked as unused using the SET UNUSED statement. This operation is allowed because it only affects previously marked unused columns, not actively used data. F. Correct. Dropping a table is allowed even if it's in read-only mode because it is a DDL operation that does not operate on the rows of the table but rather on the object itself.

The behavior of read-only tables and the operations that can be performed on them are detailed in the Oracle Database SQL Language Reference and Oracle Database Administrator's Guide.

In Oracle SQL, when performing a JOIN operation, the ON clause is used to specify the condition that relates the two tables being joined. The WHERE clause can be used to further filter the result set.

A) This is a valid join condition using the WHERE clause to filter the rows after the join has been made.

B) This statement will fail because the ON clause should only contain conditions that relate the two tables. The condition for filtering the departments table should be in the WHERE clause, not in the ON clause. This is a common mistake when writing JOIN statements.

C) This is a correct statement. The ON clause specifies how the tables are related and the WHERE clause specifies an additional filtering condition for the query.

D) This statement is also correct. It's similar to the first statement (A) and properly places the department_id filter in the ON clause, which is acceptable though not typically best practice as it can be less readable than using a WHERE clause for non-join conditions.

When the JOIN operation is executed, the database first pairs rows from the joined tables that meet the join condition specified by the ON clause. Then, it filters the result of the JOIN operation based on the condition specified in the WHERE clause.

References:

Oracle Documentation on Joins: https://docs.oracle.com/database/121/SQLRF/queries006.htm#SQLRF52359

A. True. When using set operators, the number and order of columns must be the same in all SELECT statements involved in the query. The data types of those columns must also be compatible.

E. True. The FOR UPDATE clause cannot be specified in a subquery or a SELECT statement that is combined with another SELECT statement by using a set operator.

B is incorrect because the column names do not need to match; only the number and data types of the columns must be compatible. C is incorrect because only the final SELECT statement in the sequence of UNION/INTERSECT/MINUS operations can have an ORDER BY clause. D is incorrect because, as of Oracle 12c, UNION ALL can be used with CLOB columns, but UNION, INTERSECT, and MINUS cannot.

Oracle's interval data types store a period of time. When you want to format an interval as a string, you can use the TO_CHAR function.

A. This statement will not execute successfully because TO_DATE expects a string representing a date, not a number derived from an interval.

B. This statement will not execute successfully because TO_NUMBER does not support interval data types as an input.

C. This statement will not execute successfully because TO_DATE does not support interval data types as an input.

D. This statement will not execute successfully because TO_NUMBER expects a number or a string representing a number as an argument, not a date.

E. This statement will execute successfully. TO_CHAR function can be used to convert interval values to a formatted string, such as 'HH24:MM'.

The actions possible using the ALTER TABLE command:

E. Rename a table: The ALTER TABLE command can be used to rename a table, although the syntax typically involves RENAME TO as part of table management.

F. Enable or disable constraints on a table: This is a standard use of the ALTER TABLE command, allowing for constraints to be enabled or disabled, which is critical for managing table integrity during data loads or maintenance.

Incorrect options:

A: You cannot drop pseudo columns from a table as they are not explicitly defined or managed like regular columns.

B: The ALTER TABLE command does not directly restrict DML statements; this would typically be managed through security roles or other database mechanisms.

C: Dropping all columns from a table simultaneously is not possible; a table must retain at least one column.

D: Locking a set of rows is performed with SQL commands like SELECT FOR UPDATE, not with ALTER TABLE.

In Oracle 12c SQL, the GROUP BY clause is used to arrange identical data into groups with the GROUP BY expression followed by the SELECT statement. The SUM() function is then used to calculate the sum for each grouped record on a specific column, which in this case is the salary column.

Option A is valid because it correctly applies the GROUP BY clause. Both dept_id and join_date are included in the SELECT statement, which is a requirement when using these columns in conjunction with the GROUP BY clause. This means that the query will calculate the sum of salaries for each combination of dept_id and join_date. It adheres to the SQL rule that every item in the SELECT list must be either an aggregate function or appear in the GROUP BY clause.

Option B is invalid due to a typo in SELECT depe_id and also because it ends with a colon rather than a semicolon.

Option C is invalid because you cannot nest aggregate functions like MAX(AVG(salary)) without a subquery.

Option D is invalid for the same reason as option C, where it tries to nest aggregate functions AVG(MAX(salary)), which is not allowed directly in SQL without a subquery.

For further reference, you can consult the Oracle 12c documentation, which provides comprehensive guidelines on how to use the GROUP BY clause and aggregate functions like SUM():

Oracle Database SQL Language Reference, 12c Release 1 (12.1): GROUP BY Clause

Oracle Database SQL Language Reference, 12c Release 1 (12.1): Aggregate Functions

Regarding creating tables in an Oracle database:

B. The same table name can be used for tables in different schemas: In Oracle, a schema is essentially a namespace within the database; thus, the same table name can exist in different schemas without conflict, as each schema is distinct.

C. A system privilege is required: To create tables, a user must have the necessary system privileges, typically granted explicitly or through roles such as CREATE TABLE or administrative privileges depending on the environment setup.

Incorrect options for all three repeated questions:

A: Oracle SQL does not allow specifying the maximum number of rows directly in a CREATE TABLE statement; this is controlled by storage allocation and database design rather than table creation syntax.

D: Creating an external table does not create the physical file. It merely creates a table structure that allows access to data stored in an external file specified in the directory; the file itself must already exist or be managed outside of Oracle.

E: A primary key constraint is not mandatory for creating tables. While it is a common practice to define a primary key to enforce entity integrity, it is not required by the Oracle SQL syntax for table creation.

These answers and explanations are aligned with Oracle Database 12c SQL documentation and standard practices.

B: True. The REFERENCES privilege can be granted on specific columns within a table. This is necessary when a user needs to define foreign key constraints that reference those particular columns.

C: True. The UPDATE privilege can be granted on specific columns, allowing users to update only designated columns within a table. This is useful for restricting write access to sensitive or critical data within a table.

F: True. The INSERT privilege can also be granted on specific columns, meaning a user can be permitted to insert data into only certain columns of a table. This helps in maintaining data integrity and controlling access to data fields based on user roles.