SQL中的并集与聚合

我有3个SQL查询，我想使用Union将它们合并到一个表中我尝试了不同的查询，但没有一个有效，我缺少什么

SELECT DISTINCT 
       place.type AS type, 
       COUNT(place.type)AS place,
       0 AS msd,
       0 AS county
FROM   place 
GROUP BY place.type;

SELECT DISTINCT 
       mcd.type, 
       0 AS place, 
       COUNT(mcd.type) AS msd, 
       0 AS county
FROM   mcd 
GROUP BY mcd.type;

SELECT DISTINCT 
       county.type, 
       0 AS place, 
       0 AS msd,
       COUNT(county.type) AS county
FROM   county 
GROUP BY county.type;

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因此，最终输出将是方案（类型、地点、mcd、县）其中，type包含3个表中类型的所有不同值，place包含type值在place表中出现的次数，mcs和country的出现次数相同。

您需要一个外部查询来从三个查询组合中获取

type

值

下面是一个示例，使用UNION ALL set运算符组合三个查询的结果。该查询是一个内联视图，由外部查询引用，外部查询对类型列执行GROUP by，对计数/0列执行SUM AGGRATE

  SELECT t.type
       , SUM(t.place)
       , SUM(t.msd)
       , SUM(t.county)
    FROM ( SELECT place.type AS type
                , COUNT(place.type) AS place
                , 0 AS msd
                , 0 AS county
             FROM place
            GROUP BY place.type
            UNION ALL
           SELECT mcd.type
                , 0 AS place
                , COUNT(mcd.type) AS msd
                , 0 AS county
             FROM mcd
            GROUP BY mcd.type
            UNION ALL
           SELECT county.type
                , 0 AS place
                , 0 AS msd
                , COUNT(county.type) AS county
             FROM county
            GROUP BY county.type
         ) t
     GROUP BY t.type

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对于每个查询中的

GROUPBY

子句，不需要DISTINCT关键字

将3个表连接在一起似乎更适合您的要求

SELECT coalese(place.type,mcd.type,conty.type) AS type, 
       COUNT(place.type)AS place,
       COUNT(mcd.type) AS msd, 
       COUNT(county.type) AS county
FROM   place 
FULL OUTER JOIN   mcd    ON place.type = mcd.type
FULL OUTER JOIN   county ON place.type = county.type 
GROUP BY coalese(place.type,mcd.type,conty.type)

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您会收到什么错误消息？在查询之间添加

联合时有什么问题？我认为这应该行得通。但是，
不同的
不是必需的。