写一段SQL语句要求是能计算李贺何李白的年龄，并且计算出两个值的差

假设有一个名为`poet`的表，其中包含诗人的姓名和出生年份(`birth_year`)字段，可以使用以下SQL语句计算李贺和李白的年龄，并计算两者年龄的差：

SELECT 
    '李贺' AS poet_name, 
    YEAR(NOW()) - birth_year AS poet_age 
FROM poet 
WHERE poet_name = '李贺'
UNION
SELECT 
    '李白' AS poet_name, 
    YEAR(NOW()) - birth_year AS poet_age 
FROM poet 
WHERE poet_name = '李白';

这将返回一个类似于以下内容的结果：

+----------+----------+
| poet_name| poet_age |
+----------+----------+
| 李贺     |       138|
| 李白     |       133|
+----------+----------+

要计算两个年龄之间的差，请使用以下SQL语句：

SELECT 
    ABS(p1.poet_age - p2.poet_age) AS age_difference 
FROM 
    (SELECT 
        YEAR(NOW()) - birth_year AS poet_age 
    FROM poet 
    WHERE poet_name = '李贺') AS p1, 
    (SELECT 
        YEAR(NOW()) - birth_year AS poet_age 
    FROM poet 
    WHERE poet_name = '李白') AS p2;

这将返回一个包含两个年龄之间差值的行：

+----------------+
| age_difference |
+----------------+
|               5|
+----------------+