Sql Query：Union All with Top

Question

我想从两个select语句中获得一个组合输出。

首先选择返回某个索引的对象。 第二个选择返回最近的对象。

  declare @h geometry select @h = Geom from obj where ObjectIndex = 15054
  select ObjectIndex, Geom.STDistance(@h) from obj where ObjectIndex = 15054 
  union all
  select top( 1) ObjectIndex, Geom.STDistance(@h) from  obj WITH(index(idx_Spatial)) where Geom.STDistance(@h) < 0.0004 
  and ObjectLayerName = 'Up_Layer' order by Geom.STDistance(@h) 

不幸的是，第二个语句返回了错误的对象。我期望最近的对象，但它返回第二个最接近的实例。 但是，当我只执行第二个select语句时，它返回正确的对象。

 select top( 1) ObjectIndex, Geom.STDistance(@h) from  obj WITH(index(idx_Spatial)) where Geom.STDistance(@h) < 0.0004 
  and ObjectLayerName = 'Up_Layer' order by Geom.STDistance(@h) 

感谢您的帮助。

Answer 1

Order by将在UNION之后应用，尝试类似这样的内容

DECLARE @h GEOMETRY

SELECT @h = Geom
FROM   obj
WHERE  ObjectIndex = 15054

SELECT ObjectIndex,
       Geom.Stdistance(@h) dist
FROM   obj
WHERE  ObjectIndex = 15054
UNION ALL
SELECT ObjectIndex,
       dist
FROM  (SELECT TOP( 1) ObjectIndex,
                      Geom.Stdistance(@h) AS dist
       FROM   obj WITH(INDEX(idx_Spatial))
       WHERE  Geom.Stdistance(@h) < 0.0004
              AND ObjectLayerName = 'Up_Layer'
       ORDER  BY Geom.Stdistance(@h)) a
ORDER  BY dist