根据子表显示主表内容问题

[ajdkjalj]

DECLARE @t TABLE (id INT PRIMARY KEY, Name NVARCHAR(20))
INSERT INTO @t VALUES (1,'王五')
INSERT INTO @t VALUES (2,'王二')
DECLARE @c TABLE (childid INT PRIMARY KEY,id int, age NVARCHAR(20))
INSERT INTO @c VALUES (1,1,'3')
INSERT INTO @c VALUES (2,1,'')
INSERT INTO @c VALUES (3,2,'2')

select * from @t
select * from @c

@t主表，@c子表，这里我要查询主表，根据子表最后一条记录age是否为空，查询时显示有年龄，没有年龄。这里主表id为1，子表最后一条记录为2,1,''，为空，显示没有年龄，主表id为2，子表对应不为空，显示有年龄

我要得到的结果
id name result
1 王五 没有年龄
2 王二 有年龄

[二月十六]

DECLARE @t TABLE (id INT PRIMARY KEY, Name NVARCHAR(20))
INSERT INTO @t VALUES (1,'王五')
INSERT INTO @t VALUES (2,'王二')
DECLARE @c TABLE (childid INT PRIMARY KEY,id int, age NVARCHAR(20))
INSERT INTO @c VALUES (1,1,'3')
INSERT INTO @c VALUES (2,1,'')
INSERT INTO @c VALUES (3,2,'2')

SELECT  [@t].id ,
        Name ,
        CASE WHEN c.age <>0 THEN '有年龄'
             ELSE '没有年龄'
        END AS result
FROM    @t
        JOIN ( SELECT   * ,
                        ROW_NUMBER() OVER ( PARTITION BY id ORDER BY childid DESC ) AS num
               FROM     @c
             ) c ON c.id = [@t].id
                    AND c.num = 1

[文盲老顾]

select * from @t a
cross apply (select top 1 (case when datalength(age)>0 then '有年龄：'+age else '无年龄' end) as result from @c where id=a.id order by childid desc) app

[小野马1209]

如有年龄是Null值，可在条件判断是改成 when B.age is Null

select A.ID,A.Name,
case when 
B.age=='' then '没有年龄'
else '有年龄'
end as result
from @t A
inner join @c B ON B.id=A.id