select语法错误

[lsqzx000]

SELECT XS FROM YS_DAA041 C WHERE C.JH=YS_DAA041.JH AND C.XJXH=0 AND C.TGMC=YS_DAA041.TGMC

这一句在运行的时候，提示
列前缀 'YS_DAA041' 与查询中所用的表名或别名不匹配。

应该怎么改？

[liangCK]

SELECT XS FROM YS_DAA041 C WHERE C.JH=YS_DAA041.JH AND C.XJXH=0 AND C.TGMC=C.TGMC 

[liangCK]

SELECT XS FROM YS_DAA041 C WHERE C.JH=C.JH AND C.XJXH=0 AND C.TGMC=C.TGMC 

[bqb]

SELECT XS FROM [YS_DAA041] C WHERE C.JH=[YS_DAA041].JH AND C.XJXH=0 AND C.TGMC=[YS_DAA041].TGMC 

[bqb]

SELECT * FROM [YS_DAA041], C WHERE C.JH=[YS_DAA041].JH AND C.XJXH=0 AND C.TGMC=[YS_DAA041].TGMC 

[lsqzx000]

再帮忙解释下
C.JH=YS_DAA041.JH AND C.XJXH=0 AND C.TGMC=C.TGMC
这个条件起什么作用？