Tag: databases

Questions Related to databases

In a PL/SQL block, a variable is declared as NUMBER without an initial value. What will its value be when it is first used in the executable section of the PL/SQL block?
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  1. 0

  2. NULL

  3. Results in a compilation error

  4. An exception will be raised

Show answer
Correct Option: B
Explanation:

To solve this question, the user needs to know what happens when a variable is declared in PL/SQL without an initial value.

The answer is:

B. NULL

If a variable is declared in PL/SQL without an initial value, its value will be NULL when it is first used in the executable section of the PL/SQL block. This means that the variable does not have a value assigned to it yet. If the variable is used in an expression or operation, it will result in a NULL value, which can cause unexpected behavior in your code.

Option A is incorrect because the variable will not have a value of 0 by default.

Option C is incorrect because declaring a variable without an initial value is legal and will not result in a compilation error.

Option D is incorrect because an exception will not be raised when a variable is declared without an initial value. It will simply have a value of NULL.

Functions for error trapping are contained in which section of a PL/SQL block?
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  1. Header

  2. Declarative

  3. Exception

  4. Executable

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Correct Option: C

Select the VALID trigger type(s)?

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  1. AFTER statement trigger

  2. INSERT row trigger

  3. DELETE row trigger

  4. UPDATE row trigger

Show answer
Correct Option: A

AI Explanation

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

Option A) AFTER statement trigger - This option is correct. AFTER statement triggers are valid trigger types in database systems. They are executed after a SQL statement is executed.

Option B) INSERT row trigger - This option is incorrect. INSERT row triggers are not valid trigger types. Instead, you can use an AFTER INSERT trigger or a BEFORE INSERT trigger.

Option C) DELETE row trigger - This option is incorrect. DELETE row triggers are not valid trigger types. Instead, you can use an AFTER DELETE trigger or a BEFORE DELETE trigger.

Option D) UPDATE row trigger - This option is incorrect. UPDATE row triggers are not valid trigger types. Instead, you can use an AFTER UPDATE trigger or a BEFORE UPDATE trigger.

The correct answer is A) AFTER statement trigger. This option is correct because AFTER statement triggers are valid trigger types in database systems. They are executed after a SQL statement is executed.

Which of the following statements about an SQL statement are not correct?
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  1. SQL statements are not case-sensitive, unless indicated.

  2. Keywords can be abbreviated.

  3. SQL statements can be on one or more lines.

  4. Keywords cannot be split across lines.

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Correct Option: B

What is a database cursor?
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  1. A cursor is SQL keyword specifying a retrieved data order.

  2. Cursor is acronym for Current Set Of Records and is a database object pointing to a currently selected set of records.

  3. A blinking vertical line that indicates the location of the next input on the display screen.

  4. None of the above.

Show answer
Correct Option: B
Explanation:

To solve this question, the user needs to have some understanding of databases and their operations.

Option A: This option is incorrect. The SQL keyword that specifies the order of retrieved data is "ORDER BY" and not "cursor."

Option B: This option is correct. A cursor is a database object that points to a currently selected set of records. It allows you to retrieve and manipulate data row by row. The term "cursor" comes from the idea of a cursor in a text editor, which is a movable indicator that shows where the next action will occur.

Option C: This option is incorrect. The blinking vertical line that indicates the location of the next input on the display screen is called a "cursor," but it is not related to database operations.

Option D: This option is incorrect because option B is the correct answer.

Therefore, The Answer is: B.

What does ACID stand for?
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  1. Access. Constraint. Index. Data.

  2. Atomicity. Consistency. Isolation. Durability.

  3. Access. Consistency. Isolation. Data.

  4. None of the above

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Correct Option: B

Select incorrect variable declarations
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  1. foo_text varchar2(10) := 'hello world';

  2. foo_char char(1) := 'Y';

  3. foo_number varchar2(10);

  4. foo_text number(10);

Show answer
Correct Option: A
Explanation:

The incorrect variable declarations are A

  • A. foo_text varchar2(10) := 'hello world'; is incorrect because the variable foo_text is declared as a varchar2 type, but the initial value 'hello world' is a string. A varchar2 type can only store a sequence of characters, while a string can store a sequence of characters and other special characters, such as spaces and symbols.

The correct variable declarations are B, C, D.

  • B. foo_char char(1) := 'Y'; is correct because the variable foo_char is declared as a char type, which is a special type of varchar2 type that can only store a single character. The initial value 'Y' is a single character, so it is a valid value for the foo_char variable.
  • C. foo_number varchar2(10); is correct because the variable foo_number is declared as a varchar2 type, which can store a sequence of characters. The initial value 'hello world' is a sequence of characters, so it is a valid value for the foo_number variable.
  • D. foo_text number(10); is correct because the variable foo_text is declared as a number type, which can store an integer

Therefore, the correct answer is A.

What command can you use to see the errors from a recently created view or stored procedure?
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  1. SHOW MISTAKES;

  2. SHOW ERRORS;

  3. DISPLAY ERRORS;

  4. DISPLAY MISTAKES;

  5. None of the above.

Show answer
Correct Option: B

What is the value of l_child_number? DECLARE l_parent_number NUMBER := 1; BEGIN DECLARE l_child_number NUMBER := 2; BEGIN l_child_number := l_parent_number + l_child_number; END; DBMS_OUTPUT.PUT_LINE(TO_CHAR(l_child_number)); EXCEPTION WHEN OTHERS THEN l_child_number := 0; DBMS_OUTPUT.PUT_LINE(TO_CHAR(l_child_number); END;
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  1. 1

  2. 2

  3. 3

  4. 0

  5. None of the above

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Correct Option: D

Which of the following is not a valid Oracle PL/SQL exception.
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  1. NO_DATA_FOUND ORA-01403

  2. DUP_VAL_ON_INDEX ORA-00001

  3. TWO_MANY_ROWS ORA-01422

  4. OTHERS

  5. None of the above. These are all valid.

Show answer
Correct Option: C
Explanation:

To solve this question, the user needs to have knowledge of Oracle PL/SQL exceptions and their syntax.

The correct answer is option C. TWO_MANY_ROWS ORA-01422 is not a valid Oracle PL/SQL exception.

Explanation for each option:

A. NO_DATA_FOUND ORA-01403: This is a valid exception in Oracle PL/SQL. It is raised when a SELECT INTO statement returns no rows.

B. DUP_VAL_ON_INDEX ORA-00001: This is a valid exception in Oracle PL/SQL. It is raised when a unique index constraint is violated.

C. TWO_MANY_ROWS ORA-01422: This is not a valid exception in Oracle PL/SQL. It is an invalid exception.

D. OTHERS: This is a valid exception in Oracle PL/SQL. It is used to catch any exception that is not explicitly handled.

E. None of the above. These are all valid: This option is incorrect as option C is not a valid exception.

Therefore, the answer is: C.