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

For SQL queries involving set operations like UNION, UNION ALL, INTERSECT, and MINUS, the data types and number of columns in the SELECT statements being combined must be the same. Here is a breakdown of each query option:

Option A: This query successfully combines results from two tables using UNION ALL, which combines all rows from both SELECT statements, including duplicates. Both queries select two columns (prod_id and exp_date, with exp_date being NULL in the second query). This is valid as the number of columns and their data types match.

Option B: This query attempts to use INTERSECT, which returns only the rows common to both SELECT statements. However, the first SELECT statement chooses prod_id and prod_name, while the second only substitutes a constant value for prod_id without specifying from which table it selects prod_name. If "newproducts" (presumably a typo and should be "new_products") does not have the exact columns as "products", or if the data types do not match, it will fail.

Option C: This query uses UNION, which removes duplicates from the combined dataset. The use of SELECT * assumes that both "products" and "new_products" tables have the same columns in the same order with matching data types. This query will succeed if those conditions are met.

Option D: This query uses MINUS to subtract results of the second SELECT from the first. However, it fails because 'k' does not explicitly match a column name in "products", suggesting a potential error unless 'k' is indeed a valid column.

Option E: This query fails because the first SELECT statement fetches only one column (prod_id) while the second fetches two columns (prod_id and prod_name). UNION ALL requires the same number of columns with compatible types in all SELECT statements involved.

The INTERSECT operator in SQL returns the results that are common to both of the SELECT statements. It functions similarly to a set intersection in mathematics. When comparing rows for the INTERSECT operation, Oracle Database uses all the expressions in the SELECT lists to derive the result set. NULL values are considered equal for the INTERSECT operator.

Evaluating the provided data from the ORDERS and INVOICES tables, let's see which rows have the same ORDER_ID and ORDER_DATE in both tables:

A: Order ID 3 has a NULL order date in the ORDERS table and does not match with any row in the INVOICES table, so it will not be returned.

B: Order ID 2 has a NULL order date in the ORDERS table but has a non-NULL order date in the INVOICES table, so it will not be returned.

C: Order ID 1 has a NULL order date in both tables, but INTERSECT considers NULLs as equal, so this will be returned.

D: Order ID 5 has a date of 01-MAR-2019 in the ORDERS table and 01-APR-2019 in the INVOICES table, so it will not be returned since the dates do not match.

E: Order ID 4 has a date of 01-FEB-2019 in both tables, so this row will be returned as it matches in both.

F: Order ID 3 has a NULL order date in the ORDERS table but has 01-JAN-2019 in the INVOICES table, so it will not be returned.

Based on this analysis, the query will return:

Order ID 1 with a NULL order date.

Order ID 4 with an order date of 01-FEB-2019.

So the correct answer is:

D. only &mgr_id: Since the hiredate variable is already defined before the SELECT statement, you will not be prompted for &hiredate again. However, &mgr_id has not been defined, so you will be prompted for this substitution variable.

The SQL LIKE operator is used in a WHERE clause to search for a specified pattern in a column. Here are the evaluations of the options:

A: The pattern ' % a % ’ will match any customer names that contain the letter 'a' anywhere in the name, not necessarily those starting with 'Ma'.

B: This is correct as 'Ma%' will match any customer names that start with 'Ma'.

C: In SQL, the wildcard character is '%' not '*', therefore, the pattern 'Ma' is incorrect.

D: This is the correct syntax. 'UPPER (customer_ name ) LIKE 'MA%'' will match customer names starting with 'Ma' in a case-insensitive manner.

E: Again, '*' is not a valid wildcard character in SQL.

F: The character '&' is not a wildcard in SQL.

G: The operator 'KIKE' is a typo, and '.Ma' is not valid SQL pattern syntax.

In Oracle Database 12c, the INTERSECT operator is used in compound queries to return only the rows that are common to both SELECT statements involved in the query. Here's a breakdown of why the correct answer is C:

A: Incorrect. The order of the tables in an INTERSECT operation does not affect the output because INTERSECT returns only the common elements between the two queries. The operation is symmetric.

B: Incorrect. While the column names themselves can differ between the two SELECT statements, the data types and the number of columns must match for INTERSECT to function correctly.

C: Correct. INTERSECT returns the intersection of the results of the two queries, which includes only rows that are found in both result sets.

D: Incorrect. The number of columns and their data types in each SELECT statement of the INTERSECT must be the same to avoid errors and to correctly perform the comparison.

E: Incorrect. INTERSECT does not ignore NULLs; rows with NULL values in corresponding columns must exactly match (both sides having NULLs in the same column) to be included in the output.

When comparing the performance of different SQL join types and conditions, Oracle SQL optimizations generally ensure that performance is consistent across different syntactical forms of expressing the same logic:

Option A: False. The BETWEEN condition does not inherently perform worse than using >= and <=. Oracle's optimizer typically evaluates these conditions similarly, optimizing the underlying execution based on the data distribution and available indexes.

Option B: False. Oracle's optimizer is designed to handle both Oracle-specific join syntax and ANSI join syntax with equal competence. Performance differences would typically be negligible because the optimizer translates both into an optimal execution plan based on the same underlying mechanisms.

Option C: True. The join syntax used (whether Oracle's traditional syntax or ANSI standard syntax) generally does not affect the performance. Oracle's query optimizer is adept at translating different syntaxes into efficient execution plans.

Option D: False. The assertion that BETWEEN always performs better than >= and <= is incorrect. Performance depends more on factors like indexing, the specific data and distribution, and the Oracle optimizer's capabilities than on the mere choice of syntax.

Option E: False. While table aliases help improve query readability and can prevent ambiguity in SQL queries, they do not inherently improve performance. Their use is a best practice for code clarity and maintenance, not performance enhancement.

Understanding Oracle's data dictionary views is crucial for database management:

Option C: USER_TABLES displays all tables owned by the current user.

USER_TABLES is a view that shows all tables owned by the user executing the query.

Option F: All users can query DBA_TABLES successfully.

While all users can attempt to query DBA_TABLES, only users with the appropriate privileges can retrieve information from it. This option is tricky; "querying" is possible for all, but "retrieving data" depends on privileges.

Options A, B, D, and E are not entirely correct:

Option A and Option E are incorrect because USER_TABLES shows tables regardless of SELECT privileges.

Option B is incorrect; one does not need SELECT privileges on each table to view them in DBA_TABLES, but they need appropriate system privileges to access DBA_TABLES.

Option D is incorrect as ALL_TABLES displays tables accessible to the current user, not just owned by them.

For external tables in Oracle:

C. DML statements cannot be used on them: External tables are read-only in Oracle. They allow access to data in external sources as if it were within a table in the database, but they do not support DML operations (INSERT, UPDATE, DELETE).

D. Their data can be retrieved by using only SQL or PL/SQL: You can query the data in external tables using SQL or PL/SQL, just as you would with regular database tables.

Incorrect options are:

A: You cannot create indexes directly on external tables.

B: External tables cannot be populated using the CREATE TABLE AS SELECT command since they are primarily meant for accessing data stored outside the database.

E: Only the metadata of an external tables is stored in the database; the actual data remains in external files.

A. This statement is incorrect. An INVISIBLE index is maintained during DML operations just like a VISIBLE index. The difference is that an INVISIBLE index is not used by the optimizer unless explicitly hinted. B. This statement is correct. When creating a table, you can define indexes on one or more columns as part of the table definition. C. This statement is incorrect. While a DROP INDEX statement will drop the index, it does not always prevent updates to the table. If the index is marked as unusable or is an invisible index, for example, updates can still be performed. D. This statement is correct. It is possible to have both a UNIQUE index and a non-unique index on the same column. The UNIQUE index enforces the uniqueness of column values, while the non-unique index does not. E. This statement is correct to some extent. Descending indexes are not function-based indexes per se, but they are indexes on which the data is sorted in descending order, as opposed to the default ascending order. However, descending indexes are conceptually related to function-based indexes because they alter the way the indexed data is stored. F. This statement is incorrect. The use of an index in query execution depends on the optimizer's decision, which is based on statistics and the cost associated with using the index. There are situations where the optimizer may choose a full table scan even if there is an index on the filter column.

References can be found in the Oracle Database Concepts Guide and the SQL Language Reference documentation, which detail the behavior of indexes and how they are managed within the Oracle database.

C. True. A transaction that is interrupted by a system failure is automatically rolled back by Oracle to ensure data consistency. This is part of the ACID (Atomicity, Consistency, Isolation, Durability) properties that Oracle adheres to.

D. True. A ROLLBACK without specifying a savepoint rolls back the entire transaction and removes all savepoints within that transaction. This restores the data to the state it was in at the beginning of the transaction.