sql - 在 FULL JOIN 中添加多列，假设空行为零

Question

我运行 PostgreSQL，我有多个(10 多个)具有相同列名和格式的表，我想对其中两个列求和。 如果其中一个表中缺少一行，我需要将其视为 0(零)。

双表示例:

表A:

primkey | year | month | day | data_value
--------+------+-------+-----+-----------
20120101| 2012 |  01   |  01 |    3.7
20120102| 2012 |  01   |  02 |    1.0

表B:

primkey | year | month | day | data_value
--------+------+-------+-----+-----------
20120101| 2012 |  01   |  01 |    1.3
20120103| 2012 |  01   |  03 |    5.5

想要的输出:

primkey | year | month | day | data_value
--------+------+-------+-----+-----------
20120101| 2012 |  01   |  01 |    5.0
20120102| 2012 |  01   |  02 |    1.0
20120103| 2012 |  01   |  03 |    5.5

我正在考虑这样做:

SELECT a.primkey, a.year, a.month, a.day, a.data_value+b.data_valueas data_value FROM "TableA" as a FULL JOIN "TableB" as b ON a.primkey = b.primkey;

但它会产生这个(缺少一些 data_values):

primkey | year | month | day | data_value
--------+------+-------+-----+-----------
20120101| 2012 |  01   |  01 |    5.0
20120102| 2012 |  01   |  02 |    
20120103| 2012 |  01   |  03 |   

注意:primkey 是唯一的并且是 PRIMARY KEY，这需要对连接 10+ 表有效

Answer 1

SELECT COALESCE(a.primkey, b.primkey) AS primkey
  , COALESCE(a.year, b.year)          AS year
  , COALESCE(a.month, b.month)        AS month
  , COALESCE(a.day, b.day)            AS day
  , COALESCE(a.data_value,0) + COALESCE( b.data_value, 0) AS data_value
FROM "TableA" AS a
FULL JOIN "TableB" AS b ON a.primkey = b.primkey
   ;