1z0-071 Exam Dumps : Oracle Database 12c SQL

C. True, the names of the columns in each SELECT statement of an INTERSECT query do not need to match, as long as the data types and order of the columns correspond.D. True, the INTERSECT operator returns only the rows that are common to both SELECT statements, effectively acting as a set intersection of the results from both queries.

References:

Oracle documentation on INTERSECT operator: Oracle Database SQL Language Reference

Detailed behavior of INTERSECT: Oracle Compound Queries

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.

In Oracle SQL, the following syntactical rules apply:

A. This query will result in an error because there is no comma separating the column names FIRST_NAME and LAST_NAME. The correct syntax should include a comma to separate the column names in the SELECT list.

B. This query is correctly formatted with a comma separating the column names, so it will not result in an error.

C. This query will result in an error because an alias defined in the SELECT list (ANNUAL_SALARY) cannot be used in the WHERE clause of the same query level. It must be repeated in the WHERE clause as 12 * SALARY.

D. This query will execute successfully because 12 * SALARY is directly used in the WHERE clause, and ANNUAL_SALARY is used in the ORDER BY clause, which is allowed.

E. This query is correct and will not result in an error. It uses 12 * SALARY in both the WHERE and ORDER BY clauses.

F. Similar to option C, this query will execute successfully because ANNUAL_SALARY is correctly used in the ORDER BY clause, and the WHERE clause does not attempt to reference the alias.

References:

Oracle Database SQL Language Reference, 12c Release 1 (12.1): "Database Object Names and Qualifiers"