在Oracle数据库中，可以使用以下几种方法来获取大值：

1、使用MAX函数：

语法：SELECT MAX(column_name) FROM table_name;

示例：SELECT MAX(salary) FROM employees;

2、使用子查询：

语法：SELECT column_name FROM table_name WHERE column_name = (SELECT MAX(column_name) FROM table_name);

示例：SELECT salary FROM employees WHERE salary = (SELECT MAX(salary) FROM employees);

3、使用ORDER BY和ROWNUM限制：

语法：SELECT column_name FROM table_name WHERE rownum <= 1 ORDER BY column_name DESC;

示例：SELECT salary FROM employees WHERE rownum <= 1 ORDER BY salary DESC;

4、使用LIMIT子句（适用于Oracle 12c及更高版本）：

语法：SELECT column_name FROM table_name ORDER BY column_name DESC FETCH FIRST 1 ROW ONLY;

示例：SELECT salary FROM employees ORDER BY salary DESC FETCH FIRST 1 ROW ONLY;

5、使用聚合函数和GROUP BY子句（适用于有多个最大值的情况）：

语法：SELECT column_name, MAX(column_name) AS max_value FROM table_name GROUP BY column_name;

示例：SELECT department, MAX(salary) AS max_salary FROM employees GROUP BY department;

这些方法可以根据具体的需求选择适合的方式来获取大值。