这个为什么提示语法错误？
select xmbh, xmmc, cast(fbsj as varchar) FROM tdcrjbxx WHERE (iffb = '1 ')
union all
(select CAST(id AS VARCHAR(50)) xmbh,title xmmc,addtime fbsj FROM tdjy_news where cataid=13)

上面的没有错

但是这样就报错了

select * from
(
select xmbh, xmmc, cast(fbsj as varchar) FROM tdcrjbxx WHERE (iffb = '1 ')
union all
(select CAST(id AS VARCHAR(50)) xmbh,title xmmc,addtime fbsj FROM tdjy_news where cataid=13)
)

WHY?

[解决办法]
select * from
(
select xmbh, xmmc, cast(fbsj as varchar) as col1 FROM tdcrjbxx WHERE (iffb = '1 ')
union all
(select CAST(id AS VARCHAR(50)) xmbh,title xmmc,addtime fbsj FROM tdjy_news where cataid=13)
) t
[解决办法]
cast(fbsj as varchar) fbsj