update B set B.B=A.A,B.C=A.A from A where A.ID=B.ID
-------------------
update B set B.B=convert(varchar,A.A,121),B.C=convert(varchar,A.A,121) from A where A.ID=B.ID
什么数据库呀?
如果是 SQL Server 的话
UPDATE
B
SET
B.B = A.A, B.C = A.A
FROM
B JOIN A ON ( B.ID = A.ID )