Oracle 多表数据修改有关问题

Oracle 多表数据修改问题
现有SQL语句

SQL code

UPDATE (SELECT a.volumeid, a.volume, a.newcasenum, b.casenum,               b.volumeid AS str          FROM volume a, propdat b         WHERE a.volumeid IS NULL AND a.volume = b.casenum)   SET volumeid = str

括号里查询结果显示为
VOLUMEIDVOLUMENEWCASENUMCASENUMSTR

nullF-7-12779610135046F-7-1277656424162
nullF-7-12779610135046F-7-1277656424162
nullF-7-12779610135046F-7-1277656424162
nullF-7-12779610135046F-7-1277656424162
nullF-7-12779610135046F-7-1277656424162
nullF-7-12779610135046F-7-1277656424162

现在想把str的数值赋值到volumeid里 报错

报错提示为cannot modify a column which maps to a non key-preserved tabl
求大神们给个可以解决方法或代码的SQL语句 怎么才能蒋STR里的值赋值到volumeid里 谢谢


[解决办法]
试试这个呢

SQL code

UPDATE   volume a   SET   volumeid =            (SELECT   b.volumeid               FROM   propdat b              WHERE       a.volumeid IS NULL                      AND a.volume = b.casenum                      AND ROWNUM = 1) WHERE   EXISTS (SELECT   1                   FROM   propdat c                  WHERE   a.volumeid IS NULL AND a.volume = c.casenum)