how to use if else of in sql code example

Example 1: else if sql server

IF (Expression 1)
BEGIN
   Statement 1;
END

ELSE IF (Expression 2)
BEGIN
   Statement 2;
END
..........
ELSE 
BEGIN
   Default Statement;
END

Example 2: SQL IF ELSE

SELECT CASE             
            WHEN A + B > C AND B + C > A AND A + C > B THEN
                CASE 
                    WHEN A = B AND B = C THEN 'Equilateral'
                    WHEN A = B OR B = C OR A = C THEN 'Isosceles'
                    ELSE 'Scalene'
                END
            ELSE 'Not A Triangle'
        END
FROM TRIANGLES;