Parameters (IN, OUT, INOUT) in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does an IN parameter do in a SQL stored procedure?

An IN parameter allows you to pass a value into the stored procedure. It is used to provide input data that the procedure can use but cannot change.

beginner

What is the purpose of an OUT parameter in SQL procedures?

An OUT parameter is used to return a value from the stored procedure back to the caller. It allows the procedure to send data out after processing.

intermediate

Explain an INOUT parameter in SQL stored procedures.

An INOUT parameter acts as both input and output. It passes a value into the procedure and can also return a modified value back to the caller.

beginner

Can an IN parameter be modified inside the stored procedure?

No, an IN parameter cannot be changed inside the procedure. It is read-only and only used to provide input values.

intermediate

How do OUT and INOUT parameters differ in their usage?

OUT parameters only return values from the procedure and do not accept input. INOUT parameters accept input and can also return modified values.

Which parameter type is used only to send data into a SQL stored procedure?

A OUT

B INOUT

C IN

D RETURN

IN parameters are used to pass input values into the procedure.

What type of parameter allows a stored procedure to return a value back to the caller?

A OUT

B DECLARE

C INOUT

D IN

OUT parameters are designed to send values back from the procedure.

Which parameter type can both accept input and return output?

A VAR

B OUT

C IN

D INOUT

INOUT parameters work as input and output parameters.

Can an IN parameter be changed inside the procedure?

A Yes, always

B No, it is read-only

C Only if declared as INOUT

D Only in some SQL dialects

IN parameters are read-only inside the procedure.

If you want to modify a value inside a procedure and send it back, which parameter type should you use?

A INOUT

B OUT

C IN

D CONST

INOUT parameters allow modification and returning of values.

Describe the differences between IN, OUT, and INOUT parameters in SQL stored procedures.

Think about how data flows in and out of the procedure.

Explain why you might choose an INOUT parameter instead of separate IN and OUT parameters.

Consider when input needs to be changed and sent back.

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