SQLserver 数据库中update select from 语句

错误的：

UPDATE TJ_TJXMB n
SET n.DJ = SELECT
    b.unit_price
FROM
    his_system_cure_item_info b
WHERE
    b.item_name = n.MC

error错误

[Err] 42000 - [SQL Server]Incorrect syntax near 'n'.

正确的；

UPDATE TJ_TJXMB 
SET DJ = b.unit_price
FROM
    his_system_cure_item_info b,TJ_TJXMB n
WHERE
    b.item_name = n.MC