UPDATE SCM_CGFHD2 B SET B.KAIPIAOSHU=A.AMOUNT FROM SCM_tuihuodiaozhengdan2 A WHERE B.BILLID IN(SELECT BILLID FROM SCM_CGFHDHEAD WHERE NO='FH201208012669') AND A.BILLID IN(SELECT BILLID FROM SCM_tuihuodiaozhengdanHEAD WHERE NO='FH201208000006' ) AND B.KUANHAO=A.KUANHAO AND B.WULIAO=A.WULIAO AND B.GUIGE=A.GUIGE AND B.CHICUN=A.CHICUN AND B.XINYANSE=A.XINYANSE

.....你这写的完全是错误的。。。。
SET B.KAIPIAOSHU = (),括号里面select出
KAIPIAOSHU 要等于的值，最后在加个where 语句。。。。