sql问题

下面这段语句为什么加上KINMU_GOKEI.TY_JIKAGAI就报00797的错？？请大侠指点。浪哥在么？

SELECT KINMU_GOKEI.TY_JIKAGAI
,TO_CHAR(Count(KINMU_DAIKYU.NENGETSU),'99.9')
from KINMU_MONTHLY
LEFT JOIN KINMU_GOKEI ON KINMU_GOKEI.IDCODE='861000' AND KINMU_GOKEI.KIGYO_CODE='1030' AND KINMU_GOKEI.NENGETSU=KINMU_MONTHLY.NENGETSU
LEFT JOIN KINMU_DAIKYU ON KINMU_DAIKYU.IDCODE='861000' AND KINMU_DAIKYU.KIGYO_CODE='1030' AND KINMU_DAIKYU.NENGETSU=KINMU_MONTHLY.NENGETSU
LEFT JOIN KINMU_DAITAI ON KINMU_DAITAI.IDCODE='861000' AND KINMU_DAITAI.KIGYO_CODE='1030' AND KINMU_DAITAI.NENGETSU=KINMU_MONTHLY.NENGETSU
WHERE  KINMU_MONTHLY.IDCODE='861000' AND KINMU_MONTHLY.KIGYO_CODE='1030'
GROUP BY KINMU_DAIKYU.NENGETSU ORDER BY KINMU_DAIKYU.NENGETSU DESC ;

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KINMU_GOKEI.TY_JIKAGAI  不是GROUP BY 格式吧

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什么是GROUP BY 格式？？？

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你仔细看看
SELECT KINMU_GOKEI.TY_JIKAGAI
,TO_CHAR(Count(KINMU_DAIKYU.NENGETSU),'99.9')
from KINMU_MONTHLY
GROUP BY KINMU_DAIKYU.NENGETSU ORDER BY KINMU_DAIKYU.NENGETSU DESC ;

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吐血中.....大哥不要卖关子了！！！！！

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实验数据

SQL> select *  from student;
        ID    CLASSNO NAME
---------- ---------- ------------------
        1