条件增加后返回的记录数反而多了，为什么呢？

[jamespro]

SELECT count(schoolid) AS s1 ,sum(a7) as s2 ,sum(a8) as s3 ,sum(a11) as s4 ,sum(a12) as s5,sum(a16) as s6
FROM [TABLE A]
WHERE a9<>'' and a9 is not null
语句结束后返回1226条


SELECT count([TABLE A].schoolid) AS s1 ,sum(a7) as s2 ,sum(a8) as s3 ,sum(a11) as s4 ,sum(a12) as s5,sum(a16) as s6
FROM [TABLE A],[TABLE B]
WHERE [TABLE B].schooltype like 'D%'
and [TABLE A].a9<>''
and [TABLE A].a9 is not null
and [TABLE B].schoolsys=[TABLE A].schoolid
语句结束后返回1239条

请问多出来13条是怎么回事？

[wzh1215]

第二个语句跟第一个不一样，第二个你用了联合查询，两个表数据联合查询比单表查询的数据多很正常也！

[Rotaxe]

因为你用了两表联接，记录多是正常的

[victorycyz]

tableB中有重复的学校。

[cht99]

你的tableB中的schoolsys和tableA中的schoolid不是一对一的关系，tableB中的schoolsys字段应该有重复数据吧？