Mastering Conditional Logic: CASE, IF, ELSE

Definition

Conditional Logic refers to programming constructs that allow you to execute specific actions based on whether a condition is true or false. The most common forms are IF, ELSE, and CASE statements.

Example:
In a simple scenario, if a student’s score is above 60, they pass; otherwise, they fail.

• IF the score is greater than 60, THEN the student passes.
• ELSE the student fails.

Explanation

IF Statement

• Purpose: Executes a block of code if a specified condition is true.
• Syntax (in SQL):

  IF condition THEN
      -- code to execute
  END IF;
  

Example:

IF score > 60 THEN
    SELECT 'Pass';
END IF;

ELSE Statement

• Purpose: Provides an alternative block of code to execute when the IF condition is false.
• Syntax (in SQL):

  IF condition THEN
      -- code if true
  ELSE
      -- code if false
  END IF;
  

Example:

IF score > 60 THEN
    SELECT 'Pass';
ELSE
    SELECT 'Fail';
END IF;

CASE Statement

• Purpose: Evaluates a list of conditions and returns a corresponding result. Useful for multiple conditions.
• Syntax (in SQL):

  CASE 
      WHEN condition1 THEN result1
      WHEN condition2 THEN result2
      ELSE default_result
  END CASE;
  

Example:

SELECT 
    CASE 
        WHEN score >= 90 THEN 'A'
        WHEN score >= 80 THEN 'B'
        WHEN score >= 70 THEN 'C'
        WHEN score >= 60 THEN 'D'
        ELSE 'F'
    END AS Grade
FROM Students;

Key Differences

• IF/ELSE is typically used for binary decisions (true/false).
• CASE is more efficient for evaluating multiple conditions in a single statement.

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Real-World Applications

• Finance: Determining credit scores based on income and debt levels.
• Healthcare: Assigning risk levels to patients based on various health metrics.
• E-commerce: Personalizing user experiences based on purchase history or browsing behavior.

Challenges

• Complexity: Overusing nested IF statements can lead to confusing code.
• Performance: CASE statements can be more efficient than multiple IF/ELSE statements in SQL for large datasets.

Best Practices

• Keep conditions simple and clear.
• Use CASE for multiple conditions to improve readability.
• Test conditions thoroughly to avoid logical errors.

Practice Problems

Bite-Sized Exercises

1. Write an IF statement that checks if a number is even or odd.
2. Create a CASE statement that assigns a discount based on purchase amount:
   • 0-100: No discount
   • 101-500: 10% discount
   • 501+: 20% discount

Advanced Problem

Using a SQL database of employees, write a query that categorizes employees based on their years of service:

• Less than 1 year: "New"
• 1-5 years: "Junior"
• 6-10 years: "Mid-Level"
• More than 10 years: "Senior"

Instructions:

1. Open your SQL environment.
2. Create a table named Employees with columns Name and YearsOfService.
3. Insert sample data.
4. Write the CASE statement to categorize employees.

YouTube References

To enhance your understanding of conditional logic, search the Ivy Pro School’s YouTube channel using these terms:

• “SQL IF ELSE Statements Ivy Pro School”
• “SQL CASE Statement Ivy Pro School”
• “Conditional Logic in Python Ivy Pro School”

Reflection

• How can you apply conditional logic in your current projects or job?
• Have you encountered situations where using CASE could simplify your code?
• What challenges do you foresee when implementing these statements in larger systems?

Summary

• IF statements execute code based on a true condition.
• ELSE provides an alternative for false conditions.
• CASE allows for evaluating multiple conditions efficiently.
• Use these constructs to improve decision-making in your code and streamline processes in various industries.