Parameters (IN, OUT, INOUT) in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an input parameter named 'user_id' of type INT.

SQL

CREATE PROCEDURE GetUserName([1] INT) BEGIN SELECT name FROM users WHERE id = user_id; END;

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

AIN user_id

BOUT user_id

CINOUT user_id

DPARAM user_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using OUT or INOUT instead of IN for input parameters.

Forgetting to specify the parameter mode.

The IN keyword declares an input parameter that passes a value into the procedure.

2fill in blank

medium

Complete the code to declare an output parameter named 'total_count' of type INT.

SQL

CREATE PROCEDURE CountUsers([1] INT) BEGIN SELECT COUNT(*) INTO total_count FROM users; END;

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AVAR total_count

BOUT total_count

CINOUT total_count

DIN total_count

Attempts:

3 left

💡 Hint

Common Mistakes

Using IN instead of OUT for output parameters.

Not using INTO clause to assign value to output parameter.

The OUT keyword declares an output parameter that returns a value from the procedure.

3fill in blank

hard

Fix the error in the procedure declaration by choosing the correct parameter mode for 'balance'.

SQL

CREATE PROCEDURE UpdateBalance(IN user_id INT, [1] balance DECIMAL(10,2)) BEGIN SET balance = balance + 100; END;

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

AINOUT

BOUT

CIN

DVAR

Attempts:

3 left

💡 Hint

Common Mistakes

Using IN when the parameter value needs to be changed inside the procedure.

Using OUT when the parameter needs an initial input value.

The INOUT keyword allows the parameter to be used for both input and output, so the procedure can read and modify 'balance'.

4fill in blank

hard

Fill both blanks to declare an INOUT parameter 'score' of type INT and assign it a new value inside the procedure.

SQL

CREATE PROCEDURE AdjustScore([1] score INT) BEGIN SET score [2] score + 10; END;

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

AINOUT

B=

C+=

DOUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using OUT instead of INOUT for parameters that need initial values.

Using += which is not valid in SQL for assignment.

INOUT allows the parameter to be read and updated. The = operator assigns the new value.

5fill in blank

hard

Fill all three blanks to declare an OUT parameter 'result', assign it a value, and select it after procedure execution.

SQL

CREATE PROCEDURE CalculateSum(IN a INT, IN b INT, [1] result INT) BEGIN SET result [2] a + b; END; CALL CalculateSum(5, 10, @sum); SELECT [3];

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

AOUT

B=

C@sum

DINOUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using IN or INOUT instead of OUT for output parameters.

Forgetting to use session variables to get output values after CALL.

OUT declares the output parameter. = assigns the sum. @sum is the session variable used to retrieve the output value.

Practice

1. What does the IN parameter type in a SQL stored procedure do?

easy

A. It allows the procedure to send output values only.

B. It allows the procedure to receive input values only.

C. It allows the procedure to both receive input and send output.

D. It declares a variable inside the procedure.

Solution

1. Step 1: Understand parameter types in SQL procedures

   Parameters can be IN, OUT, or INOUT. IN means input only.

2. Step 2: Identify the role of IN parameters

   IN parameters pass values into the procedure but do not return values.

3. Final Answer:

   It allows the procedure to receive input values only. -> Option B

4. Quick Check:

   IN = input only [OK]

Hint: IN means input only, no output from procedure [OK]

Common Mistakes:

• Confusing IN with OUT or INOUT
• Thinking IN parameters can return values
• Assuming IN declares internal variables

2. Which of the following is the correct syntax to declare an OUT parameter named result of type INT in a MySQL stored procedure?

easy

A. CREATE PROCEDURE proc_name(IN result INT)

B. CREATE PROCEDURE proc_name(INOUT result INT)

C. CREATE PROCEDURE proc_name(OUT result INT)

D. CREATE PROCEDURE proc_name(RESULT OUT INT)

Solution

1. Step 1: Recall parameter declaration syntax in MySQL

   Parameters are declared as IN, OUT, or INOUT followed by name and type.

2. Step 2: Check each option's syntax

   CREATE PROCEDURE proc_name(OUT result INT) uses correct syntax: OUT result INT. CREATE PROCEDURE proc_name(INOUT result INT) uses INOUT, not OUT. CREATE PROCEDURE proc_name(IN result INT) uses IN, not OUT. CREATE PROCEDURE proc_name(RESULT OUT INT) has wrong order and keyword.

3. Final Answer:

   CREATE PROCEDURE proc_name(OUT result INT) -> Option C

4. Quick Check:

   OUT parameter syntax = OUT name type [OK]

Hint: OUT parameters use OUT before name and type [OK]

Common Mistakes:

• Using IN instead of OUT
• Swapping parameter order
• Using wrong keywords like RESULT OUT

3. Consider this MySQL procedure call:

CALL calculate_sum(5, 10, @total);
SELECT @total;

Given the procedure signature:

CREATE PROCEDURE calculate_sum(IN a INT, IN b INT, OUT sum INT)
BEGIN
  SET sum = a + b;
END;

What will be the output of SELECT @total;?

medium

A. 5

B. Syntax error

C. NULL

D. 15

Solution

1. Step 1: Understand procedure parameters and call

   The procedure takes two input numbers and outputs their sum via the OUT parameter sum. The call passes 5 and 10 as inputs, and @total as the OUT variable.

2. Step 2: Calculate the output value

   The procedure sets sum = 5 + 10 = 15. This value is assigned to the session variable @total.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: OUT parameters update session variables after CALL [OK]

Common Mistakes:

• Expecting NULL because of no SELECT inside procedure
• Confusing IN and OUT parameters
• Not using session variables for OUT

4. You have this procedure:

CREATE PROCEDURE update_value(INOUT val INT)
BEGIN
  SET val = val + 1;
END;

Which of the following calls will correctly update the session variable @x from 10 to 11?

medium

A. CALL update_value(@x);

B. CALL update_value(10);

C. CALL update_value(INOUT @x);

D. CALL update_value(IN @x);

Solution

1. Step 1: Understand INOUT parameter usage

   INOUT parameters require a variable to pass in and receive updated value. Session variables like @x can be used.

2. Step 2: Analyze each call

   CALL update_value(@x); passes @x correctly. CALL update_value(10); passes a literal 10, which is not a variable. CALL update_value(INOUT @x); uses invalid syntax. CALL update_value(IN @x); uses IN keyword, which is incorrect for INOUT.

3. Final Answer:

   CALL update_value(@x); -> Option A

4. Quick Check:

   INOUT needs variable, not literal [OK]

Hint: Use session variables for INOUT parameters [OK]

Common Mistakes:

• Passing literals instead of variables
• Using IN or INOUT keywords in CALL
• Expecting procedure to update literals

5. You want to create a procedure that swaps two integer values using INOUT parameters a and b. Which of the following procedure bodies correctly swaps the values?

hard

A. BEGIN DECLARE temp INT; SET temp = a; SET a = b; SET b = temp; END

B. BEGIN SET a = b; SET b = a; END

C. BEGIN SET a = a + b; SET b = a - b; SET a = a - b; END

D. BEGIN SET a = b; SET b = a + b; END

Solution

1. Step 1: Understand swapping logic with INOUT parameters

   Swapping requires a temporary variable to hold one value while assigning the other.

2. Step 2: Evaluate each option's correctness

   BEGIN DECLARE temp INT; SET temp = a; SET a = b; SET b = temp; END uses a temporary variable to swap correctly. BEGIN SET a = b; SET b = a; END overwrites a before assigning b. BEGIN SET a = a + b; SET b = a - b; SET a = a - b; END uses arithmetic swap but is valid only if no overflow and no NULLs. BEGIN SET a = b; SET b = a + b; END does not swap correctly.

3. Final Answer:

   BEGIN DECLARE temp INT; SET temp = a; SET a = b; SET b = temp; END -> Option A

4. Quick Check:

   Temporary variable swap = correct [OK]

Hint: Use temp variable to swap INOUT parameters safely [OK]

Common Mistakes:

• Overwriting variables without temp
• Using arithmetic swap without checks
• Ignoring NULL or overflow risks