Purpose
The IF THEN ELSE syntax is an alternate to CASE function. 
Syntax
if::=
                                                                         
                                                                    
Usage Notes
- If the condition evaluates to true, the expression after THENis returned.
- If the condition evaluates to false, the expression after ELSEis returned, orNULLif anELSEexpression is not defined.
- If the condition evaluates to NULL/UNKNOWN, the expression returnsNULL.
Examples
Copy
                                                                
                                                            
                                                            SELECT name, age, IF age < 18 THEN 'underaged' ELSE 'adult' ENDIF AS 'LEGALITY' FROM persons;Result
| NAME | AGE | LEGALITY | 
| Alice | 25 | adult | 
| Bob | 16 | underaged | 
| Charlie | NULL | NULL | 
| David | 34 | adult |