表中有A B C三列,用SQL语句实现：当A列大于B列时选择A列否则选择B列，当B列大于C列时选择B列否则选C

1：

DELIMITER //
CREATE PROCEDURE ProcOut()
BEGIN
DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN END;
DECLARE Sum_a INT(11);
DECLARE Sum_b INT(11);
DECLARE Sum_c INT(11);

-- 获取A列中的总值 <--
DECLARE cur_1 CURSOR FOR SELECT SUM(A) FROM table_name;
OPEN cur_1;
FETCH cur_ 1 INTO Sum_a;
CLOSE cur_1;

-- 获取B列中的总值 <--
DECLARE cur_2 CURSOR FOR SELECT SUM(B) FROM table_name;
OPEN cur_2;
FETCH cur_ 2 INTO Sum_b;
CLOSE cur_2;

-- 获取C列中的总值 <--
DECLARE cur_3 CURSOR FOR SELECT SUM(C) FROM table_name;
OPEN cur_3;
FETCH cur_ 3 INTO Sum_c;
CLOSE cur_3;

IF Sum_a > Sum_b THEN
SELECT A FROM table_name;

ELSEIF Sum_b > Sum_c THEN
SELECT B FROM table_name;

ELSE
SELECT C FROM table_name;
END IF;;
END;//

CALL ProcOut()//

2：

select

case

when A>B then

case when A>C then A

else C end

else

case when B>C then B else C

end

end as name

from member

3:
select
(case when A>B then A else B end) as 'A’ ,
(case when B>C then B else C end) as 'B' from Person;