Using If else in SQL Select statement

Handling complex logic

The true strength of the CASE statement is its ability to handle multiple conditions and return values based on them. This effectively allows you to nest if-else structures within your SQL SELECT clause. Here’s an extended example:

SELECT 
  Name, 
  Age,
  CASE 
    WHEN Age < 18 THEN 'Minor' 
    WHEN Age BETWEEN 18 AND 65 THEN 'Adult' 
    ELSE 'Senior' 
  END AS AgeGroup -- "You're only as old as your data"
FROM 
  Users;
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Dive deeper: Multiple CASE expression in one statement

Now, let's explore how to combine multiple different conditions in a single SELECT clause, each corresponding to a unique CASE expression, to give your SQL a dash of multitasking valor:

SELECT 
  EmployeeID,
  CASE WHEN PerformanceScore > 80 THEN 'Exceeds Expectations' ELSE 'Meets Expectations' END AS PerformanceRating, -- "Performance anxiety?"
  CASE WHEN Sales > 10000 THEN 'Top Seller' ELSE 'Contributor' END AS SalesStatus -- "Who's the 'sellionaire' now?"
FROM 
  Employees;


The above example clearly emphasizes how each CASE encapsulates and parses a different aspect of an employee's profile, offering a multi-faceted view of your data.

Optimization and Best Practices

Following best practices while orchestrating CASE statements can significantly enhance your SQL's performance and readability:

1. Be specific with column names to avoid confusion in complex queries.
2. Designate a catchy alias for your CASE expressions to improve result interpretation.
3. Remember to neatly close each CASE statement with an END to avoid being cornered by syntax errors.
4. Consider encapsulating complex conditions into functions to streamline your code.

Keep in mind, CASE can only return a single scalar value for every row in your result.

Watch out for pitfalls

Dealing with NULL values

NULL values can often be overlooked causing unexpected behavior. Here's how to make peace with them:

SELECT 
  PlayerName, 
  CASE 
    WHEN Score IS NULL THEN 'No Score' -- "Null is the new high score!"
    WHEN Score >= 100 THEN 'High Score'
    ELSE 'Low Score'
  END AS PlayerStatus
FROM 
  GameScores;


Not skipping the ELSE

Including the ELSE clause provides a safety net that ensures a default value is returned when none of the conditions match, preventing unwanted NULL results during runtime.