Sql 多个表的“按日期分组”

（我正在使用postgres）

我有两个来自不同表的查询。每个都按日期分组。 将它们联接到一个查询（联合或联接）的最佳方式是什么？ 提前谢谢

质疑№1：

SELECT to_char(date,'MM') as mon,
       extract(year from date) as yyyy,
       SUM("table_1"."user_money") AS user_sum,
       SUM("table_1"."system_money") AS system_sum
FROM "table_1"
GROUP BY 1,2
ORDER BY 2,1;

 mon | yyyy |     user_sum     |   system_sum    
-----+------+------------------+-----------------
 11  | 2015 |        10        |       50        
 12  | 2015 |        20        |       60        
(2 rows)

查询结果№1：

SELECT to_char(date,'MM') as mon,
       extract(year from date) as yyyy,
       SUM("table_1"."user_money") AS user_sum,
       SUM("table_1"."system_money") AS system_sum
FROM "table_1"
GROUP BY 1,2
ORDER BY 2,1;

 mon | yyyy |     user_sum     |   system_sum    
-----+------+------------------+-----------------
 11  | 2015 |        10        |       50        
 12  | 2015 |        20        |       60        
(2 rows)

质疑№2：

SELECT to_char(created_at,'MM') as mon,
       extract(year from created_at) as yyyy,
       SUM("table_2"."amount") AS payments_sum
FROM "table_2"
GROUP BY 1,2
ORDER BY 2,1;

 mon | yyyy | payments_sum
-----+------+--------------     
 10  | 2015 |     500      
 11  | 2015 |     600      
 12  | 2015 |     700      
 01  | 2016 |     800      
(4 rows)

查询结果№2：

SELECT to_char(created_at,'MM') as mon,
       extract(year from created_at) as yyyy,
       SUM("table_2"."amount") AS payments_sum
FROM "table_2"
GROUP BY 1,2
ORDER BY 2,1;

 mon | yyyy | payments_sum
-----+------+--------------     
 10  | 2015 |     500      
 11  | 2015 |     600      
 12  | 2015 |     700      
 01  | 2016 |     800      
(4 rows)

所需结果：

 mon | yyyy | payments_sum |     user_sum     |   system_sum   
-----+------+--------------+------------------+----------------
 10  | 2015 |     500      |                  |                
 11  | 2015 |     600      |        10        |       50       
 12  | 2015 |     700      |        20        |       60      
 01  | 2016 |     800      |                  |                
(4 rows)

试试这个

SELECT 
    to_char(date,'MM') as mon,
    extract(year from date) as yyyy,
    SUM("table_2"."amount") AS payments_sum,
    SUM("table_1"."user_money") AS user_sum,
    SUM("table_1"."system_money") AS system_sum
FROM 
    "table_1"
LEFT JOIN 
    "table_2" ON (to_char("table_1"."date", 'MM') = to_char("table_2"."date", 'MM') AND extract(year from "table_1"."date") = extract(year from "table_2"."date"))
GROUP BY 1,2
ORDER BY 2,1;

---

我认为您可以将每个查询视为子查询，然后与完整的外部联接相结合。联盟可能不是你想要的

大概是这样的：

SELECT * FROM
(SELECT to_char(date,'MM') as mon,
   extract(year from date) as yyyy,
   SUM("table_1"."user_money") AS user_sum,
   SUM("table_1"."system_money") AS system_sum
FROM "table_1"
GROUP BY 1,2) AS q1
FULL OUTER JOIN 
(SELECT to_char(created_at,'MM') as mon,
   extract(year from created_at) as yyyy,
   SUM("table_2"."amount") AS payments_sum
FROM "table_2"
GROUP BY 1,2) AS q2
ON q1.mon = q2.mon AND q1.yyyy = q2.yyyy
ORDER BY 2,1

---

在mon和yyyy值匹配的位置进行连接。

这里是另一个更符合PostgreSQL特定语法的连接：

WITH query_one AS (
    SELECT 
        to_char(date,'MM') as mon,
        extract(year from date) as yyyy,
        SUM("table_1"."user_money") AS user_sum,
        SUM("table_1"."system_money") AS system_sum
    FROM 
        "table_1"
    GROUP BY 
        1,2
), query_two AS (
    SELECT 
        to_char(created_at,'MM') as mon,
        extract(year from created_at) as yyyy,
        SUM("table_2"."amount") AS payments_sum
    FROM 
        "table_2"
    GROUP BY 
        1,2
)
SELECT
    *
FROM
    query_one
    LEFT JOIN query_two USING (mon, yyyy)
ORDER BY 
    yyyy
    , mon;

---

USING

子句更易于使用，可以防止

mon

和

yyyy

在输出中出现两次，其余的只是为了清晰地查看。两个表中是否都有一列可以相互链接？@AndreasSchmidt没有，我想你的选项是最好的，它工作得很好，谢谢！因为在其他情况下是的，我们需要删除重复的列，然后对空日期使用COALESCE和NULLIF