Procedure parameters (IN, OUT, INOUT) in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an input parameter in a MySQL stored procedure.

MySQL

CREATE PROCEDURE AddNumbers([1] num1 INT, num2 INT)
BEGIN
  SELECT num1 + num2 AS sum_result;
END;

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

AVAR

BOUT

CINOUT

DIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using OUT or INOUT instead of IN for input parameters.

Omitting the parameter mode keyword.

The IN keyword declares an input parameter for the procedure. It means the value is passed into the procedure.

2fill in blank

medium

Complete the code to declare an output parameter in a MySQL stored procedure.

MySQL

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

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

AIN

BINOUT

COUT

DVAR

Attempts:

3 left

💡 Hint

Common Mistakes

Using IN instead of OUT for output parameters.

Trying to assign values to IN parameters inside the procedure.

The OUT keyword declares an output parameter. It allows the procedure to return a value to the caller.

3fill in blank

hard

Fix the error in the procedure parameter declaration to allow both input and output.

MySQL

CREATE PROCEDURE UpdateScore(playerId INT, [1] score INT)
BEGIN
  SET score = score + 10;
END;

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

AINOUT

BOUT

CIN

DVAR

Attempts:

3 left

💡 Hint

Common Mistakes

Using IN or OUT alone when both input and output are needed.

Trying to modify an IN parameter inside the procedure.

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

4fill in blank

hard

Fill both blanks to declare an IN parameter and an OUT parameter in a procedure.

MySQL

CREATE PROCEDURE CalculateTax([1] amount DECIMAL(10,2), [2] tax DECIMAL(10,2))
BEGIN
  SET tax = amount * 0.15;
END;

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

AIN

BOUT

CINOUT

DVAR

Attempts:

3 left

💡 Hint

Common Mistakes

Using OUT for the first parameter or IN for the second parameter.

Omitting parameter modes.

The first parameter is input only (IN), and the second parameter is output only (OUT).

5fill in blank

hard

Fill all three blanks to declare an IN parameter, an OUT parameter, and an INOUT parameter in a procedure.

MySQL

CREATE PROCEDURE AdjustValues([1] inputVal INT, [2] outputVal INT, [3] inoutVal INT)
BEGIN
  SET outputVal = inputVal * 2;
  SET inoutVal = inoutVal + 5;
END;

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

AIN

BOUT

CINOUT

DVAR

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up parameter modes or omitting them.

Trying to modify IN parameters inside the procedure.

The first parameter is input only (IN), the second is output only (OUT), and the third is both input and output (INOUT).

Practice

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

easy

A. It declares a variable inside the procedure without passing values.

B. It passes a value into the procedure but does not allow changes to be sent back.

C. It allows both passing a value in and sending a changed value back.

D. It allows the procedure to send a value back to the caller only.

Solution

1. Step 1: Understand the role of IN parameters

   IN parameters are used to pass values into a procedure. They act like input-only variables.

2. Step 2: Clarify output behavior of IN parameters

   Changes to IN parameters inside the procedure do not affect the caller's variables; they are input-only.

3. Final Answer:

   It passes a value into the procedure but does not allow changes to be sent back. -> Option B

4. Quick Check:

   IN = input only [OK]

Hint: IN means input only, no output changes sent back [OK]

Common Mistakes:

• Thinking IN parameters can send data back
• Confusing IN with OUT or INOUT
• Assuming IN parameters can be modified outside

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

easy

A. CREATE PROCEDURE myProc(param OUT INT) BEGIN END;

B. CREATE PROCEDURE myProc(INOUT param INT) BEGIN END;

C. CREATE PROCEDURE myProc(OUT param INT) BEGIN END;

D. CREATE PROCEDURE myProc(param INT OUT) BEGIN END;

Solution

1. Step 1: Recall correct parameter declaration order

   In MySQL, the parameter mode (IN, OUT, INOUT) comes before the parameter name and type.

2. Step 2: Check each option's syntax

   CREATE PROCEDURE myProc(OUT param INT) BEGIN END; uses 'OUT param INT' which is correct. Placing OUT after the parameter name or type is invalid syntax.

3. Final Answer:

   CREATE PROCEDURE myProc(OUT param INT) BEGIN END; -> Option C

4. Quick Check:

   Parameter mode before name and type [OK]

Hint: Parameter mode (IN/OUT/INOUT) always comes first [OK]

Common Mistakes:

• Placing OUT after parameter name or type
• Mixing parameter mode with data type
• Omitting BEGIN and END block

3. Consider this procedure call and definition:

CREATE PROCEDURE addValues(IN a INT, INOUT b INT, OUT c INT)
BEGIN
  SET b = b + a;
  SET c = a + b;
END;

CALL addValues(5, @varB, @varC);

If @varB is initially 10, what will be the values of @varB and @varC after the call?

medium

A. @varB = 15, @varC = 20

B. @varB = 10, @varC = 15

C. @varB = 5, @varC = 10

D. @varB = 15, @varC = 10

Solution

1. Step 1: Understand parameter roles and initial values

   a = 5 (IN), b = 10 (INOUT), c is OUT (initially NULL). INOUT means b can be read and updated.

2. Step 2: Calculate new values inside procedure

   SET b = b + a = 10 + 5 = 15; SET c = a + b = 5 + 15 = 20.

3. Final Answer:

   @varB = 15, @varC = 20 -> Option A

4. Quick Check:

   INOUT b updated, OUT c set correctly [OK]

Hint: INOUT changes persist; OUT must be set inside procedure [OK]

Common Mistakes:

• Assuming INOUT parameter does not change
• Confusing OUT parameter initial value
• Ignoring that OUT must be assigned inside procedure

4. Given this procedure:

CREATE PROCEDURE testProc(INOUT x INT)
BEGIN
  SET x = x + 1;
END;

Which of the following calls will cause an error?

medium

A. CALL testProc(@varX); -- @varX is a session variable

B. CALL testProc(NULL);

C. SET @varX = 10; CALL testProc(@varX);

D. CALL testProc(5);

Solution

1. Step 1: Understand INOUT parameter requirements

   INOUT parameters require a variable to pass by reference, so the procedure can read and modify it.

2. Step 2: Analyze each call

   CALL testProc(5); passes a literal (5), which is not a variable, causing an error. The other options pass variables or NULL variables, which are allowed.

3. Final Answer:

   CALL testProc(5); -> Option D

4. Quick Check:

   INOUT needs variable, not literal [OK]

Hint: INOUT requires variable, not constant literal [OK]

Common Mistakes:

• Passing literals to INOUT parameters
• Confusing INOUT with IN parameters
• Assuming NULL literal is invalid for INOUT

5. You want to create a procedure that takes two numbers, adds them, and returns the sum and the product. Which parameter types should you use for the inputs and outputs?

hard

A. IN for both inputs, OUT for sum and product outputs

B. INOUT for inputs, IN for outputs

C. OUT for inputs, IN for outputs

D. IN for inputs, INOUT for outputs

Solution

1. Step 1: Identify input and output roles

   The two numbers are inputs only, so they should be IN parameters. The sum and product are results to send back, so they should be OUT parameters.

2. Step 2: Match parameter types to roles

   IN parameters accept input values; OUT parameters return output values. INOUT is for parameters used as both input and output, which is not needed here.

3. Final Answer:

   IN for both inputs, OUT for sum and product outputs -> Option A

4. Quick Check:

   Inputs = IN, Outputs = OUT [OK]

Hint: Use IN for inputs, OUT for outputs to separate roles clearly [OK]

Common Mistakes:

• Using INOUT unnecessarily for outputs
• Confusing OUT as input
• Using IN for output parameters