1z0-071 Oracle Database 12c SQL Free Practice Exam Questions (2025 Updated)

Regarding single-row subqueries:

A. THEY CAN BE USED in the where clause: Single-row subqueries can be used in the WHERE clause to compare a column's value against the result of the subquery.

B. A SQL STATEMENT MAY HAVE MULTIPLE SINGLE ROW SUBQUERY BLOCKS: It is possible to use more than one single-row subquery within a SQL statement, each potentially in different parts of the statement (e.g., SELECT clause, WHERE clause).

E. THEY CAN BE USED IN THE HAVING CLAUSE: Similar to the WHERE clause, single-row subqueries can also be used in the HAVING clause to filter groups based on a condition evaluated against a subquery result.

Incorrect options are:

C and D: There is no such limitation on the placement of single-row subqueries relative to the comparison operator; they can be used on either side.

F: Single-row subqueries must return exactly one row to avoid errors, but they do not necessarily have to return a row; if no row is returned, the query may still execute, potentially returning no rows in the outer query.

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 the context of SQL statements using SET operations like UNION in Oracle Database 12c:

A. The data type of each column returned by the second query must be implicitly convertible to the data type of the corresponding column returned by the first query. This is correct. Oracle allows the union of columns as long as their data types are implicitly convertible, not necessarily identical.

C. The number, but not names, of columns must be identical for all SELECT statements in the query. This is correct. For a UNION operation to be valid, all SELECT statements involved must have the same number of columns, although their names and exact data types need not match.

Options B, D, and E are incorrect:

B is incorrect because exact data type matches are not required, only that they be implicitly convertible.

D is also incorrect for the same reason as B; it's enough that the types are compatible, not identical.

E is incorrect as the names

The || operator is used in Oracle SQL to concatenate strings, and the q quote operator allows you to use alternative quoting mechanisms to avoid conflicts with single quotes within a string.

In options A, B, C, D, E, and F, the q-quote operator is used in different ways to define string literals.

The correct use of the q quote operator requires the format q'[...]', where [...] is the quote delimiter of your choice and can be any single character such as {, [, (, <, or others.

Option D is the correct answer because it follows the correct syntax for the q quote operator and concatenates the literal string correctly with the value of PROD_ID.

Here is the corrected syntax from option D:

SELECT PROD_ID || q'[('s not available)]' "CURRENT AVAILABILITY" FROM product_status WHERE status = 'OUT OF STOCK';

This query will execute successfully and is the only one that correctly uses the q quote operator.

The provided SQL statement is an update statement that involves a subquery which is correlated to the main query.

A. The subquery is executed before the UPDATE statement is executed. (Incorrect)

This statement is not accurate in the context of correlated subqueries. A correlated subquery is one where the subquery depends on values from the outer query. In this case, the subquery is executed once for each row that is potentially updated by the outer UPDATE statement because it references a column from the outer query (o.customer_id).

B. All existing rows in the ORDERS table are updated. (Incorrect)

Without a WHERE clause in the outer UPDATE statement, this would typically be true. However, the correctness of this statement depends on the actual data and presence of matching customer_id values in both tables. If there are rows in the ORDERS table with customer_id values that do not exist in the CUSTOMERS table, those rows will not be updated.

C. The subquery is executed for every updated row in the ORDERS table. (Correct)

Because the subquery is correlated (references o.customer_id from the outer query), it must be executed for each row to be updated in the ORDERS table to get the corresponding cust_last_name from the CUSTOMERS table.

The behavior of data insertion into a table with a specific numeric format in Oracle Database 12c can be explained as follows:

A. INSERT INTO rate_list VALUES (-.9) inserts the value as -.9: This is correct. The value -.9 is within the precision defined by the table column (NUMBER(6,2)), where 6 is the total number of digits (including both sides of the decimal point), and 2 is the number of digits after the decimal point.

E. INSERT INTO rate_list VALUES (0.551) inserts the value as .55: Oracle rounds the number to the nearest value that fits the specified scale of 2. Thus, 0.551 rounds down to 0.55.

References:

Oracle Database SQL Language Reference 12c, particularly sections on data types and numeric precision.

For question 134, the correct options are B and F based on the capabilities and design of SQL:

B. It best supports relational databases: SQL is fundamentally designed to manage and query data in relational databases. It is the standard language used for managing relational database management systems (RDBMS) and for performing all types of data operations within them.

F. It provides independence for logical data structures being manipulated from the underlying physical data storage: SQL allows users to interact with the data at a logical level without needing to know how the data is physically stored. This is known as logical data independence, which is a key feature of SQL in managing databases.

Other options are incorrect because:

A: SQL itself doesn't guarantee ACID properties; these are provided by the database management system's transaction control mechanisms.

C, D, E: These statements are incorrect as SQL does not inherently support object-oriented concepts like encapsulation and polymorphism, is not limited to hierarchical data storage, and is not the only language used for both relational and object-oriented databases.

The LOCALTIMESTAMP function in Oracle Database returns the current date and time in the session time zone. Given that the session time zone was set to -5:00 with the ALTER SESSION SET TIME_ZONE command, LOCALTIMESTAMP will return the date and time adjusted to this session time zone.

The SYSDATE function, on the other hand, returns the current date and time from the operating system of the database server, which is not affected by the session time zone setting. In the result shown, SYSDATE returns 11-JUL-2019 11:00:00, which reflects the system time zone, not the session time zone.

The time difference between the DBTIMEZONE (+00:00) and the session time zone (-5:00) is 5 hours. Since SYSDATE shows the time as 11:00:00 in the system time zone, the LOCALTIMESTAMP adjusted to the session time zone would show the time as 06:00:00.

The correct answer is A: 11-JUL-2019 6:00:00.00000000 AM – 05:00. This represents the local timestamp in the session time zone, which is 5 hours behind the DBTIMEZONE.

Please note that the exact format returned by LOCALTIMESTAMP includes the fractional seconds up to 9 decimal places, and the time zone offset is specified as part of the timestamp.

Query B will return the highest salary in the table without grouping by department. It simply selects the maximum value for the salary column across the entire table.

Query C and D are incorrect because the GROUP BY clause will return the highest salary for each department, not the single highest salary in the entire table.

Query E is incorrect because MAX(MAX(salary)) is not a valid use of aggregate functions and will result in an error.

References:

Oracle Documentation on Aggregate Functions: Aggregate Functions

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.

D. True, after setting the DEPARTMENT_ID column to UNUSED, you can add a new column with the name DEPARTMENT_ID to the EMPLOYEES table. The UNUSED clause does not delete the column, it only marks it as no longer being used.E. True, once a column is marked as UNUSED, you cannot make updates to it. It becomes inaccessible for DML operations.

A, B, C, and F are not correct because: A. Once a column is set to UNUSED, it is not available for queries. B. The storage space is not immediately released after issuing a COMMIT; instead, the actual removal and space reclamation happen when you subsequently issue the DROP UNUSED COLUMNS operation. C. The DEPARTMENT_ID column is not set to null; instead, it's marked as UNUSED, which means it is no longer available for use. F. UNUSED columns are not placed into the recycle bin; they are just marked for deletion, and space can be reclaimed with the DROP UNUSED COLUMNS command.

References:

Oracle documentation on ALTER TABLE: Oracle Database SQL Language Reference

Understanding ALTER TABLE SET UNUSED: Oracle Database Administrator’s Guide

Queries that will execute successfully given the PRODUCT_STATUS table:

C. SELECT prod_id || q'('s not available)' "CURRENT AVAILABILITY" FROM product_status WHERE status = 'OUT OF STOCK';This query will execute successfully because it uses the q quote operator correctly to handle the inclusion of single quotes in the string.

D. SELECT prod_id || q'('s not available)' FROM product_status WHERE status = 'OUT OF STOCK';Similar to the previous query, it uses the q quote operator correctly and will execute without syntax errors.

Options A, B, E, and F are incorrect because of the incorrect or incomplete use of the quote operator:

A is incorrect because it has an additional single quote before the FROM clause.

B is incorrect because of a missing ending single quote after the q quote operator.

E and F are incorrect because they both use the q quote operator incorrectly; q’(’s not available)' is not a valid use of the quote operator, and q"'s not available" incorrectly uses double quotes instead of single quotes.

The SQL query must find all customers with last names starting with A or B, regardless of case, and a credit limit below 1000:

B. WHERE (INITCAP(cust_last_name) LIKE ‘A%' OR INITCAP(cust_last_name) LIKE ‘B%') AND cust_credit_limit < 1000: The INITCAP function initializes the first letter to uppercase for comparison. However, it should be noted that using INITCAP is not necessary when using the LIKE operator with a wildcard % following a single character, because it will not correctly filter all last names that start with an upper or lower case A or B.

D. WHERE (UPPER(cust_last_name) LIKE 'A%’ OR UPPER(cust_last_name) LIKE ‘B%’) AND cust_credit_limit < 1000: This correctly filters last names beginning with A or B in any case and includes only those with a credit limit below 1000. The UPPER function is used to convert cust_last_name to uppercase before comparison.

References:

Oracle Database SQL Language Reference 12c, especially sections on string functions and conditions.

The correct way to compute the total annual compensation, which includes the monthly salary and the monthly commission (if any), is:

Option C: SELECT last_name, (monthly_salary * 12) + (monthly_salary * 12 * NVL(monthly_commission_pct, 0)) AS annual_comp FROM employees;

This statement takes the monthly salary and multiplies it by 12 to get the annual salary, and then adds the annual commission which is the monthly salary multiplied by the commission percentage (if any, else 0) and then by 12.

Options A, B, and D are incorrect because:

Option A: Does not handle the case where the commission percentage is NULL which would result in NULL for the entire expression when added to the monthly salary.

Option B: Does not consider that the commission percentage might be NULL which could lead to incorrect calculations (or NULL values if commission is NULL).

Option D: Incorrectly adds the monthly commission percentage directly to the annual salary without considering that the percentage needs to be applied to the salary.

Oracle synonyms are used to simplify the referencing of complex schema objects:

Option A: Incorrect. A synonym cannot have another synonym; it directly references the base object.

Option B: Incorrect. A synonym does not have an object number as it is merely an alias for another object.

Option C: Correct. Any user with sufficient privileges can create a public synonym, which is accessible to all users in the database.

Option D: Incorrect. All private synonym names must be unique within a schema but not across the entire database.

Option E: Correct. Synonyms can be created for objects within packages, such as procedures or functions, simplifying the referencing of these objects without needing to specify the full package name.

Non-equi joins are joins where the join condition is based on something other than equality. In Oracle SQL, you can perform non-equi joins using various clauses:

A. The ON clause can be used: True, the ON clause can specify any condition for the join, including non-equijoins. It is not limited to equijoins.

E. The Oracle join syntax can be used: The traditional Oracle join syntax, which uses the WHERE clause to specify the join condition, can be used for all types of joins, including non-equijoins.

References:

Oracle Database SQL Language Reference 12c, especially the sections on join clauses including the ON clause and Oracle's proprietary join syntax.

A: This statement will not execute successfully because you cannot subtract a DAY interval from a DATE directly. SYSDATE needs to be cast to a TIMESTAMP first.

B: This statement is correct. It adds an interval of '1' DAY to the current TIMESTAMP.

C: This statement is correct. It subtracts an interval of '1' MINUTE from '1' DAY.

D: This statement will not execute successfully. In Oracle, you cannot add intervals of different date fields (DAY and MONTH) directly.

E: This statement has a syntax error with the quotes around INTERVAL and a misspelling, it should be 'INTERVAL'.

Oracle Database 12c SQL supports interval arithmetic as described in the SQL Language Reference documentation.

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.

The ORDER BY clause is used in a SELECT statement to sort the returned rows by one or more columns.

A. This clause would attempt to order by ename as if it were a numeric column, which is not correct since ename is not numeric.

B. This is the correct answer. The NVL function replaces nulls with the specified value, in this case, 0. This clause sorts by comm, with nulls considered as 0 and appearing first, followed by the actual values, and then sorts by ename.

C. This clause is incorrect because it would place null values at the end, but in the output, rows with null comm appear at the beginning.

D. This clause would sort the comm in descending order with the nulls at the end, which is not consistent with the output shown.

References:

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

Oracle Database SQL Language Reference, 12c Release 1 (12.1): "NVL Function"

Please note that the correct formatting of SQL statements and clauses is crucial for the successful execution of queries.