SQL中没有IF、ELSE语句就不能解决的简单SQL问题

SELECT column_name1, column_name2,
       CASE WHEN condition THEN result1
            ELSE result2
       END AS column_name3
FROM table_name;

SELECT column_name,
       CASE expression
           WHEN value1 THEN result1
           WHEN value2 THEN result2
           ...
           ELSE result
       END
FROM table_name;

SELECT column_name,
       CASE
           WHEN condition1 THEN result1
           WHEN condition2 THEN result2
           ...
           ELSE result
       END
FROM table_name;

CREATE PROCEDURE procedure_name (IN parameter1 INT)
BEGIN
    IF condition THEN
        -- code block
    ELSE
        -- code block
    END IF;
END;