Newly Released Oracle 1z0-071 Exam PDF

Substitution variables in Oracle are used to replace a value dynamically during the execution of SQL statements. The behavior of these variables is well-documented:

C. A substitution variable prefixed with & always prompts only once for a value in a session: This is true. In a session, when you use a single ampersand (&), SQL*Plus or SQL Developer will prompt for the value the first time the variable is encountered. The value for this variable will then be reused for the remainder of the session unless it is redefined.

D. A substitution variable can be used with any clause in a SELECT statement: Substitution variables can be placed in any part of a SQL statement, including the SELECT, WHERE, GROUP BY, ORDER BY, etc. They are not limited to any specific clause.

References:

Oracle SQL*Plus User's Guide and Reference, which discusses substitution variables.

In Oracle SQL, the ALTER TABLE statement is used to modify the definition of a table after it has been created. Specific changes are allowed depending on the current data type of the column and the data it contains.

A. You cannot change a VARCHAR2 column to NUMBER if the table contains rows with non-numeric values, which is the case with '123' as a VARCHAR2; it is a string, not a number.

B. You can reduce the size of a NUMBER column if the data will still fit within the new precision, but you cannot change a VARCHAR2 column to a smaller size if it contains values that exceed the new size limit.

C. You cannot change a NUMBER column to VARCHAR2 if the table contains rows because the existing data type of NUMBER does not match the new data type of VARCHAR2.

D. Similar to A, you cannot change the data type from VARCHAR2 to NUMBER if non-numeric data is present.

E. You can change a VARCHAR2(10) column to VARCHAR2(5) if all existing rows have values that fit within the new size, and you can change a NUMBER column to have a different scale (NUMBER(12,2)).

References:

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

When performing DML operations on a view, certain restrictions apply:

D. Views cannot be used to add or modify rows in an underlying table if the defining query of the view contains the DISTINCT keyword: If the defining query of a view contains the DISTINCT keyword, it cannot be used for certain DML operations, such as INSERT and UPDATE, because the set of rows it represents is not directly modifiable.

E. Views cannot be used to add or modify rows in an underlying table if the defining query of the view contains aggregating functions: Aggregating functions create a result that summarises multiple rows and cannot be reversed to point to a single row for modification.

F. Views cannot be used to add rows to an underlying table if the table has columns with NOT NULL constraints lacking default values which are not referenced in the defining query of the view: If a column with a NOT NULL constraint is not included in the view's defining query, and it does not have a default value, it is not possible to insert through the view because it would violate the NOT NULL constraint.

References:

Oracle Database SQL Language Reference 12c, particularly the sections on views and the restrictions on DML operations through views.

C. True, when performing a self join, aliases are used to differentiate the same table in different contexts within the same query. This helps in comparing different rows within the same table as if they were in two separate tables.D. True, the ON clause can be used in self joins to specify the conditions on which the join is based. This is a standard method for specifying join conditions in SQL.F. True, a self join can be an outer join, allowing for the inclusion of rows that do not have a matching row in the same table according to the join condition. This enhances the flexibility of data analysis and reporting.

References:

Oracle documentation on joins: Oracle Database SQL Language Reference

Details on self joins and outer joins: Oracle Joins Tutorial