CURSOR concept and usage in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a cursor named my_cursor.

SQL

DECLARE [1] CURSOR FOR SELECT * FROM employees;

Drag options to blanks, or click blank then click option'

Amy_cursor

Bcursor1

Ccur

Demp_cursor

Attempts:

3 left

💡 Hint

Common Mistakes

Using a keyword instead of a valid cursor name.

Forgetting to name the cursor.

The cursor name is declared right after the DECLARE keyword. Here, my_cursor is the correct cursor name.

2fill in blank

medium

Complete the code to open the cursor named my_cursor.

SQL

OPEN [1];

Drag options to blanks, or click blank then click option'

Aemp_cursor

Bcursor1

Ccur

Dmy_cursor

Attempts:

3 left

💡 Hint

Common Mistakes

Opening a cursor with a wrong or undefined name.

Forgetting the semicolon at the end.

To start using a cursor, you must open it by its declared name. Here, my_cursor is the correct name to open.

3fill in blank

hard

Fix the error in the FETCH statement to get data from my_cursor.

SQL

FETCH [1] INTO employee_name, employee_id;

Drag options to blanks, or click blank then click option'

Amy_cursor

Bcursor1

Ccur

Demp_cursor

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different cursor name than declared.

Forgetting to open the cursor before fetching.

The FETCH statement must use the exact cursor name declared and opened. Here, my_cursor is correct.

4fill in blank

hard

Fill both blanks to correctly close and deallocate the cursor named my_cursor.

SQL

CLOSE [1];
DEALLOCATE [2];

Drag options to blanks, or click blank then click option'

Amy_cursor

Bcursor1

Cemp_cursor

Dcur

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names in CLOSE and DEALLOCATE.

Forgetting to deallocate after closing.

Both CLOSE and DEALLOCATE statements must use the exact cursor name to properly release resources. Here, my_cursor is correct for both.

5fill in blank

hard

Fill all three blanks to declare, open, and fetch from a cursor named emp_cur.

SQL

DECLARE [1] CURSOR FOR SELECT name, id FROM employees;
OPEN [2];
FETCH [3] INTO emp_name, emp_id;

Drag options to blanks, or click blank then click option'

Aemp_cur

Bmy_cursor

Ccursor1

Dcur

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing different cursor names in the statements.

Forgetting to open the cursor before fetching.

All cursor operations must use the same cursor name. Here, emp_cur is used for declaring, opening, and fetching.

Practice

1. What is the main purpose of using a CURSOR in SQL?

easy

A. To process query results row by row

B. To speed up bulk data insertion

C. To create new tables dynamically

D. To automatically backup the database

Solution

1. Step 1: Understand what a cursor does

   A cursor allows you to handle each row returned by a query individually, instead of all at once.

2. Step 2: Compare options to cursor purpose

   Options B, C, and D describe tasks unrelated to row-by-row processing, which is the cursor's main use.

3. Final Answer:

   To process query results row by row -> Option A

4. Quick Check:

   Cursor = row-by-row processing [OK]

Hint: Remember: Cursor = handle rows one at a time [OK]

Common Mistakes:

• Thinking cursor speeds up bulk inserts
• Confusing cursor with table creation
• Assuming cursor automates backups

2. Which of the following is the correct order of cursor operations in SQL?

easy

A. DECLARE, FETCH, OPEN, CLOSE, DEALLOCATE

B. OPEN, DECLARE, FETCH, CLOSE, DEALLOCATE

C. DECLARE, OPEN, FETCH, CLOSE, DEALLOCATE

D. FETCH, DECLARE, OPEN, CLOSE, DEALLOCATE

Solution

1. Step 1: Recall the cursor lifecycle

   You first DECLARE the cursor, then OPEN it to start fetching rows, FETCH rows one by one, CLOSE it when done, and finally DEALLOCATE to free resources.

2. Step 2: Match the correct sequence

   Only DECLARE, OPEN, FETCH, CLOSE, DEALLOCATE follows this exact order. Other options mix the steps incorrectly.

3. Final Answer:

   DECLARE, OPEN, FETCH, CLOSE, DEALLOCATE -> Option C

4. Quick Check:

   Cursor lifecycle order = C [OK]

Hint: Remember: Declare first, then open, fetch, close, deallocate [OK]

Common Mistakes:

• Opening cursor before declaring
• Fetching before opening
• Not deallocating after closing

3. Given the following SQL cursor code snippet, what will be the output?

DECLARE @Name VARCHAR(50);
DECLARE name_cursor CURSOR FOR SELECT Name FROM Employees WHERE Department = 'Sales';
OPEN name_cursor;
FETCH NEXT FROM name_cursor INTO @Name;
WHILE @@FETCH_STATUS = 0
BEGIN
  PRINT @Name;
  FETCH NEXT FROM name_cursor INTO @Name;
END
CLOSE name_cursor;
DEALLOCATE name_cursor;

Assuming the Employees table has Sales department names: 'Alice', 'Bob', 'Carol'.

medium

A. Only 'Alice' is printed

B. Syntax error due to missing FETCH

C. No output because cursor is not opened

D. Alice Bob Carol (each printed on a new line)

Solution

1. Step 1: Understand cursor fetch loop

   The cursor fetches each row where Department = 'Sales'. It prints the @Name variable for each fetched row.

2. Step 2: Identify the printed names

   Since the table has 'Alice', 'Bob', and 'Carol' in Sales, all three names will be printed one by one.

3. Final Answer:

   Alice Bob Carol (each printed on a new line) -> Option D

4. Quick Check:

   Cursor prints all fetched rows [OK]

Hint: Cursor loops print all fetched rows until none left [OK]

Common Mistakes:

• Assuming only first row prints
• Forgetting to open cursor
• Confusing fetch status check

4. Identify the error in the following cursor code:

DECLARE cur CURSOR FOR SELECT Id FROM Products;
OPEN cur;
FETCH NEXT FROM cur INTO @ProductId;
WHILE @@FETCH_STATUS = 0
BEGIN
  PRINT @ProductId;
END
CLOSE cur;
DEALLOCATE cur;

medium

A. Missing FETCH NEXT inside the WHILE loop

B. Cursor not declared properly

C. Cursor not opened before fetching

D. No error, code runs fine

Solution

1. Step 1: Check fetch inside loop

   The code fetches once before the loop but does not fetch again inside the loop, causing an infinite loop.

2. Step 2: Identify missing statement

   To move to next row, FETCH NEXT must be inside the WHILE loop after PRINT.

3. Final Answer:

   Missing FETCH NEXT inside the WHILE loop -> Option A

4. Quick Check:

   Fetch inside loop needed to advance cursor [OK]

Hint: Always fetch next row inside the loop to avoid infinite loop [OK]

Common Mistakes:

• Forgetting FETCH NEXT inside loop
• Assuming one fetch is enough
• Not opening cursor before fetch

5. You want to update the salary of employees one by one using a cursor. Which approach correctly uses a cursor for this task?

hard

A. Open cursor, but never fetch rows, then update salary

B. Declare cursor for SELECT, open it, fetch each employee, update salary inside loop, close and deallocate

C. Declare cursor, but update salary before opening cursor

D. Use a single UPDATE statement without cursor for all employees

Solution

1. Step 1: Understand row-by-row update need

   When updating salaries individually, you must fetch each employee row and update inside the loop.

2. Step 2: Identify correct cursor usage

   Declare cursor for SELECT, open it, fetch each employee, update salary inside loop, close and deallocate correctly declares, opens, fetches, updates inside loop, then closes and deallocates cursor.

3. Final Answer:

   Declare cursor for SELECT, open it, fetch each employee, update salary inside loop, close and deallocate -> Option B

4. Quick Check:

   Cursor updates row-by-row inside loop [OK]

Hint: Update inside fetch loop after opening cursor [OK]

Common Mistakes:

• Trying to update before opening cursor
• Not fetching rows before update
• Using cursor but updating all at once