这句SQL语句哪里有错啊该怎么解决

UPDATE   TmpTbl       SET   ma5=        (        SELECT   AVERAGE(first)   /*AVERAGE换为AVG*/            FROM   (                SELECT   TOP   5  /*这里缺少列*/                     FROM   TmpTbl                       WHERE   ID <5                       ORDER   BY   ID   DESC                )        )    WHERE   ID=5
------解决方案--------------------
UPDATE   TmpTbl  
SET   ma5=(SELECT   AVERAGE(first)  
          FROM   (SELECT   TOP   5 first  FROM   TmpTbl   WHERE   ID <5   ORDER   BY   ID   DESC))  
WHERE   ID=5
------解决方案--------------------
UPDATE   TmpTbl  
SET   ma5=(
SELECT   AvG(first) 
  FROM   (
SELECT   TOP   5  first  
FROM   TmpTbl  
WHERE   ID <5  
ORDER   BY   ID   DESC)
)  
WHERE   ID=5