mysql - 使用 SQL 将两个表连接到一个表中

Question

晚上好

我在尝试找到连接两个表的解决方案时遇到问题:

比如我有

表 1:

Date  | Item
12/03 | aaaa
12/03 | aaaa
14/03 | bbbb
14/03 | aaaa
15/03 | cccc

表 2:

Date  | Item2
11/03 | aaaa
12/03 | aaaa
13/03 | bbbb
14/03 | aaaa
15/03 | cccc   

我想做一个计数来得到这个

Date  | Count(Item1) | Count(Item2)
11/03 | 0            | 1
12/03 | 2            | 1
13/03 | 0            | 1
14/03 | 2            | 1
15/03 | 1            | 1

到目前为止我已经试过了，但它似乎没有用，它只给我公共(public)日期:

SELECT F.DATE, COUNT(T1.Item1), COUNT(T2.Item2) FROM TABLE1 
T1 LEFT JOIN TABLE2 T2 ON T1.date=T2.date

Date  | Count(Item1) | Count(Item2)
12/03 | 2            | 1
14/03 | 2            | 1
15/03 | 1            | 1

有什么帮助吗？

谢谢

Answer 1

In the below SQL, the first inline view is computing all the counts at date level and same applies with second query. By combining the results of left join and right join between these two inline views we can combine all the common and uncommon results from both tables as you described.


        SELECT Date,
               Item1,
               Item2 
          FROM
             (  
                SELECT T1.Date AS Date,
                       COUNT(  T1.Item  ) AS Item1,                     
                       COUNT(  T2.Item  ) AS Item2  
                  FROM Table1 t1
                LEFT JOIN
                       Table2 t2  
                    ON t1.date = t2.date  
                GROUP BY t1.Date              
          UNION              
                SELECT T2.Date AS Date,
                       COUNT( T1.Item ) AS Item1,
                       COUNT( T2.Item ) AS Item2
                  FROM Table2 t2
                LEFT JOIN
                       Table1 t1   
                    ON t2.date = t1.date
                GROUP BY t2.Date
              ) A
         ORDER BY Date        
        ;

SQL Fiddle 实现:-

http://sqlfiddle.com/#!9/5b872/14