将多个查询合并为一个查询

Question

我正在尝试将多个查询合并为一个查询。有人有主意吗？

SELECT In_year，count（In_year）AS Num_Of_Year FROM INTERNSHIP GROUP BY In_year;

SELECT In_qtr，计数（In_qtr）AS Num_Of_Qtr FROM INTERNSHIP GROUP BY In_Qtr;

SELECT In_location，count（In_location）AS Num_Of_Location FROM INTERNSHIP GROUP BY In_location;

如果我自己运行这些查询中的每一个，我就会得到我在查找的结果。我的问题是我无法弄清楚如何将这3个查询合并为1，我试图梳理它们，但最终得到错误的输出。谢谢！

Answer 1

可能UNION子句和组织这一点可以做的伎俩：

SELECT 'Year' As Topic, In_year As Value, count(In_year) AS Count 
FROM INTERNSHIP 
GROUP BY In_year 

UNION ALL 

SELECT 'Qtr' As Topic, In_qtr As Value, count(In_qtr) AS Count 
FROM INTERNSHIP 
GROUP BY In_Qtr 

UNION ALL 

SELECT 'Location' As Topic, In_location As Value, count(In_location) AS Count 
FROM INTERNSHIP 
GROUP BY In_location; 

这表明它在单个查询的唯一途径，因为这三个SELECT都会有不同的行数，所以你不能添加自然形式的柱子。

Answer 2

我们可以用实习表作为驱动表“按组” SQLS其他连接：

select 
    t1.In_year, y.Num_Of_Year, 
    t1.In_qtr, q.Num_Of_Qtr, 
    t1.In_location, l.Num_Of_Location 
FROM 
    (select distinct In_year, In_qtr, In_location from INTERNSHIP) t1 
    join (SELECT In_year, count(In_year) AS Num_Of_Year FROM INTERNSHIP GROUP BY In_year) y on t1.In_year = y.In_year 
    join (SELECT In_qtr, count(In_qtr) AS Num_Of_Qtr FROM INTERNSHIP GROUP BY In_Qtr) q on t1.In_Qtr = q.In_Qtr 
    join (SELECT In_location, count(In_location) AS Num_Of_Location FROM INTERNSHIP GROUP BY In_location) l on t1.In_location = l.In_location