MYSQL--获取数字串中的最大值

mysql> use test;
Database changed
mysql> drop procedure if exists sp1;
Query OK, 0 rows affected (0.00 sec)

#create procedure using prepare
mysql> delimiter //
mysql> create procedure sp1(str varchar(1000))
    -> begin
    -> set @p=concat('select greatest(',str,')');
    -> PREPARE stmt1 FROM @p;
    -> EXECUTE stmt1 ;
    -> DEALLOCATE PREPARE stmt1;
    -> end;
    -> //
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;

#testing procedure,parameter count is arbitrary
mysql> call sp1('1,2,3,40,5,4000');
+---------------------------+
| greatest(1,2,3,40,5,4000) |
+---------------------------+
| 4000 |
+---------------------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.01 sec)

mysql> call sp1('1,2,3,40,5');
+----------------------+
| greatest(1,2,3,40,5) |
+----------------------+
| 40 |
+----------------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.01 sec)