To answer this question, let's break down the query step by step:

The given query is:

SELECT CONCAT(SUBSTR('MINDWORKS',-5,6),SUBSTR('KNOWMAX',-3,4)) FROM DUAL;

1. SUBSTR('MINDWORKS',-5,6):

   • This function extracts a substring from the string 'MINDWORKS'.
   • The starting point (-5) specifies that the substring should start from the 5th character from the end of the string.
   • The length (6) specifies that the substring should have a length of 6 characters.
   • Therefore, this expression returns 'WORKS'.

2. SUBSTR('KNOWMAX',-3,4):

   • This function extracts a substring from the string 'KNOWMAX'.
   • The starting point (-3) specifies that the substring should start from the 3rd character from the end of the string.
   • The length (4) specifies that the substring should have a length of 4 characters.
   • Therefore, this expression returns 'MAX'.

3. CONCAT(SUBSTR('MINDWORKS',-5,6),SUBSTR('KNOWMAX',-3,4)):

   • This function concatenates the two substrings obtained from the previous steps.
   • The result of the concatenation is 'WORKSMAX'.

Therefore, the correct answer is option C) WORKSMAX.

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To determine the number of columns presented after executing the given query, let's break down the query and analyze it step by step:

The query is: SELECT address1||','||address2||','||address2 "Adress" FROM employee;

Here, we are selecting three columns: address1, address2, and address2 (renamed as "Address" using the alias "Adress"). Each column is concatenated with a comma (',').

So, the query will produce three columns: address1, address2, and Address.

Therefore, the correct answer is C) 3.

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To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) Primary key access - This option involves accessing a table using the primary key. While primary key access can be efficient for retrieving a single row, it is not always the fastest method as it depends on the table's structure and data distribution.

Option B) Access via unique index - This option involves accessing a table using a unique index. Accessing a table via a unique index can be efficient for retrieving a single row. However, it may not always be the fastest method compared to other options.

Option C) Table access by ROWID - This option involves accessing a table directly using the ROWID. The ROWID is a unique identifier for each row in a table and allows for direct access to the desired row. This method is typically the fastest way to retrieve a single row as it bypasses index lookups.

Option D) Full table scan - This option involves scanning the entire table to find the desired row. This method is generally slower compared to other options, especially when retrieving a single row.

The correct answer is C) Table access by ROWID. This option is correct because it allows for direct access to the desired row, making it the fastest way for Oracle to retrieve a single row.

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To add a primary key on the STUDENT_ID column in the STUDENTS table, you can use the following statement:

D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id);

Explanation for each option:

A. ALTER TABLE students ADD PRIMARY KEY student_id; This option is incorrect because it is missing the CONSTRAINT keyword before PRIMARY KEY.

B. ALTER TABLE students ADD CONSTRAINT PRIMARY KEY (student_id); This option is incorrect because it is missing a name for the constraint. A constraint must have a unique name.

C. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY student_id; This option is incorrect because it is missing parentheses around the column name student_id.

D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id); This option is correct because it uses the correct syntax to add a constraint with a name (stud_id_pk) on the column student_id as the primary key.

E. ALTER TABLE students MODIFY CONSTRAINT stud_id_pk PRIMARY KEY (student_id); This option is incorrect because MODIFY CONSTRAINT is used to modify an existing constraint, not to add a new constraint.

The correct answer is D. ALTER TABLE students ADD CONSTRAINT stud_id_pk PRIMARY KEY (student_id). This option is correct because it adds a primary key constraint with the name stud_id_pk on the column student_id in the STUDENTS table.

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To answer this question, we need to understand the different DATETIME data types that can be used when specifying column definitions. Let's go through each option to understand which ones are correct:

Option A) TIMESTAMP - This option is correct. TIMESTAMP is a DATETIME data type that represents a date and time value.

Option B) INTERVAL MONTH TO DAY - This option is incorrect. INTERVAL MONTH TO DAY is not a DATETIME data type. It is a data type used to represent an interval of time in terms of months and days.

Option C) INTERVAL DAY TO SECOND - This option is correct. INTERVAL DAY TO SECOND is a DATETIME data type used to represent an interval of time in terms of days, hours, minutes, and seconds.

Option D) INTERVAL YEAR TO MONTH - This option is correct. INTERVAL YEAR TO MONTH is a DATETIME data type used to represent an interval of time in terms of years and months.

Option E) TIMESTAMP WITH DATABASE TIMEZONE - This option is incorrect. TIMESTAMP WITH DATABASE TIMEZONE is not a DATETIME data type. It is a TIMESTAMP data type that includes the database time zone.

The correct answers are A) TIMESTAMP, C) INTERVAL DAY TO SECOND, and D) INTERVAL YEAR TO MONTH. These three options are correct because they are DATETIME data types that can be used when specifying column definitions.

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To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) The DESCRIBE DEPT statement displays the structure of the DEPT table. This option is correct because the DESCRIBE statement is used to display the structure of a table, and in this case, it will display the structure of the DEPT table.

Option B) The ROLLBACK statement frees the storage space occupied by the DEPT table. This option is incorrect. The ROLLBACK statement is used to undo transactions and restore the database to the state it was in before the transaction was initiated. It does not free the storage space occupied by the table.

Option C) The DESCRIBE DEPT statement returns an error ORA-04043: object DEPT does not exist. This option is incorrect. Since the CREATE TABLE statement is executed before the DESCRIBE statement, the DEPT table will exist, and the DESCRIBE statement will be able to display its structure.

Option D) The DESCRIBE DEPT statement displays the structure of the DEPT table only if there is a COMMIT statement introduced before the ROLLBACK statement. This option is incorrect. The DESCRIBE statement does not depend on the presence of a COMMIT statement before the ROLLBACK statement. It will display the structure of the DEPT table regardless of whether a COMMIT statement was used or not.

The correct answer is A. The DESCRIBE DEPT statement displays the structure of the DEPT table.

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To view the object privileges granted to the user on specific columns, you should query the USER_COL_PRIVS data dictionary table.

Let's go through each option to understand why it is correct or incorrect:

Option A) USER_TAB_PRIVS_MADE - This option is incorrect because the USER_TAB_PRIVS_MADE table provides information about the object privileges the user has granted to other users, not the privileges granted to the user on specific columns.

Option B) USER_TAB_PRIVS - This option is incorrect because the USER_TAB_PRIVS table provides information about the object privileges granted to the user on tables, not specific columns.

Option C) USER_COL_PRIVS_MADE - This option is incorrect because the USER_COL_PRIVS_MADE table provides information about the column privileges the user has granted to other users, not the privileges granted to the user on specific columns.

Option D) USER_COL_PRIVS - This option is correct because the USER_COL_PRIVS table provides information about the column privileges granted to the user, including the privileges granted on specific columns of tables.

The correct answer is D. This option is correct because querying the USER_COL_PRIVS table allows you to view the object privileges granted to the user on specific columns.

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To answer this question, let's analyze the given SQL statement:

SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMP WHERE DEPARTMENT_ID = NULL;

The statement is attempting to display the employees who have not been assigned to any department. However, the statement is incorrect.

The correct comparison operator to check for a null value is not the equality operator (=), but rather the "IS NULL" operator. Therefore, option C is correct:

C. The operator in the WHERE clause should be changed to display the desired results.

The correct SQL statement should be:

SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMP WHERE DEPARTMENT_ID IS NULL;

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To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) You can use aggregate functions in any clause of a SELECT statement. - This option is incorrect because aggregate functions can only be used in the SELECT clause and in the HAVING clause of a SELECT statement.

Option B) You can use aggregate functions only in the column list of the SELECT clause and in the WHERE clause of a SELECT statement. - This option is incorrect because aggregate functions can also be used in the HAVING clause of a SELECT statement.

Option C) You can mix single row columns with aggregate functions in the column list of a SELECT statement by grouping on the single row columns. - This option is correct. When using aggregate functions, you can include both single row columns and aggregate functions in the column list of a SELECT statement by grouping on the single row columns.

Option D) You can pass column names, expressions, constants, or functions as parameters to an aggregate function. - This option is correct. Aggregate functions can take column names, expressions, constants, or functions as parameters.

Option E) You can use aggregate functions on a table, only by grouping the whole table as one single group. - This option is incorrect. Aggregate functions can be used on a table by grouping the data based on specific columns, not necessarily the whole table as one group.

Option F) You cannot group the rows of a table by more than one column while using aggregate functions. - This option is incorrect. You can group the rows of a table by more than one column while using aggregate functions. This allows for more specific aggregation based on multiple criteria.

The correct answers are Option C and Option D.

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To answer this question, we need to understand the concept of subqueries.

A subquery is a query that is nested within another query. It is used to retrieve data from one or more tables and is enclosed within parentheses.

Let's go through each option to understand which are true about subqueries:

Option A) A single row subquery can retrieve data from only one table. This statement is false. A single row subquery can retrieve data from multiple tables as long as they are related through a common column.

Option B) A SQL query statement cannot display data from table B that is referred to in its subquery unless table B is included in the main query's FROM clause. This statement is true. When a subquery references a table, that table must be included in the main query's FROM clause for the data to be displayed.

Option C) A SQL query statement can display data from table B that is referred to in its subquery without including table B in its own FROM clause. This statement is false. To display data from table B that is referred to in a subquery, table B must be included in the main query's FROM clause.

Option D) A single row subquery can retrieve data from more than one table. This statement is true. A single row subquery can retrieve data from multiple tables if they are related through a common column.

Option E) A single row subquery cannot be used in a condition where the LIKE operator is used for comparison. This statement is false. A single row subquery can be used in a condition where the LIKE operator is used for comparison.

Option F) A multiple-row subquery cannot be used in a condition where the LIKE operator is used for comparison. This statement is false. A multiple-row subquery can be used in a condition where the LIKE operator is used for comparison.

Based on the explanations above, the two true statements about subqueries are:

B. A SQL query statement cannot display data from table B that is referred to in its subquery unless table B is included in the main query's FROM clause. D. A single row subquery can retrieve data from more than one table.

Therefore, the correct answer is B and D.

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To enter the phone numbers of each of the 100 employees into the existing EMPLOYEES table, the appropriate data manipulation operation to perform is the INSERT operation.

Option A) MERGE - The MERGE operation is used to update or insert data into a target table based on a condition. It is not necessary in this scenario since we are only inserting data.

Option B) INSERT - This option is correct. The INSERT operation is used to add new rows of data into a table. In this case, we are adding the phone numbers of each employee into the table.

Option C) UPDATE - The UPDATE operation is used to modify existing data in a table. It is not necessary in this scenario since we are not modifying existing data, but rather adding new data.

Option D) ADD - The ADD operation is used to add new columns to an existing table. It is not necessary in this scenario since we are not adding a new column, but rather adding data to an existing column.

Option E) ENTER - This option is not a valid data manipulation operation in SQL. It is not applicable in this scenario.

Option F) You cannot enter the phone numbers for the existing employee records - This option is incorrect. It is possible to enter the phone numbers for the existing employee records by performing the INSERT operation.

Therefore, the correct answer is B) INSERT.

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To answer this question, you need to understand the concept of views in databases.

A view is a virtual table that is based on the result of a query. It does not store any data itself but instead retrieves data from the underlying tables whenever it is accessed.

Now let's go through each option to understand why it is correct or incorrect:

Option A) The underlying tables must have data - This option is incorrect because a view can still be executed successfully even if the underlying tables do not have data. The view will return an empty result set in such cases.

Option B) You need SELECT privileges on the view - This option is incorrect because having SELECT privileges on the view alone is not sufficient for the query to execute successfully. You also need SELECT privileges on the underlying tables from which the view is derived.

Option C) The underlying tables must be in the same schema - This option is incorrect because the underlying tables can be in different schemas and the view can still be executed successfully. The schema of the view itself is what matters.

Option D) You need SELECT privileges only on the underlying tables - This option is correct. In order to execute a query on an existing view successfully, you need to have SELECT privileges on the underlying tables from which the view is derived. This is because the view retrieves data from these tables when it is accessed.

The correct answer is D) You need SELECT privileges only on the underlying tables. This option is correct because having SELECT privileges on the underlying tables is necessary for the query on the view to execute successfully.

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