求一个SQL得查询语句

已知一个供应情况表 SPJ
有属性 供应商号码 SNO
  零件号码 PNO
  工程项目号码 JNO
  零件数量 QTY


求满足下面要求的供应商号码，该供应商供应给某个工程零件P1 的数量大于这个工程被供应的零件P1 的平均数量。

这个问题的SQL查询语句怎么写啊？

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结果呢

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SQL code:

SELECT SNO from SPJ WHERE QTY>(
SELECT AVG(QTY) from SPJ)

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[code=SQL][/code]
CREATE TABLE SPJ(SNO NVARCHAR(8),PNO NVARCHAR(8),JNO NVARCHAR(8),QTY NVARCHAR(8)
)
INSERT SPJ
SELECT N'S1',N'P1',N'J1',N'200' UNION ALL
SELECT N'S1',N'P1',N'J3',N'100' UNION ALL
SELECT N'S1',N'P1',N'J4',N'700' UNION ALL
SELECT N'S1',N'P2',N'J2',N'100' UNION ALL
SELECT N'S2',N'P1',N'J1',N'400' UNION ALL
SELECT N'S2',N'P3',N'J2',N'200' UNION ALL
SELECT N'S2',N'P3',N'J4',N'500'
GO
SELECT SNO
 from SPJ
WHERE QTY >(
SELECT AVG(CAST(QTY AS INT))
from SPJ
)
/*
SNO  
-------- 
S1
S2
S2

（所影响的行数为 3 行）
*/

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SQL code:

SQL codeSELECT SNOfrom SPJ WHERE QTY>
(SELECT AVG(QTY)from SPJ WHERE JNO='P1' AND PNO='P1' )

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SQL code

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