sql - 在 FULL OUTER JOIN 中选择非空列

Question

考虑以下表格:

Id     |   Name     |   Family
1      |   name1    |   family1
2      |   name2    |   family2

和:

Id     |   Orderr   |   Countt
1      |   order1   |   17
1      |   order2   |   18
3      |   order3   |   16

以及以下查询:

select table1.id,table1.name,table1.family,table2.orderr,table2.countt
from table1 FULL OUTER JOIN table2
on table1.id = table2.id

它返回:

Id     |   Name     |   Family    |   Orderr   |   Countt
1      |   name1    |   family1   |   order1   |    17
1      |   name1    |   family1   |   order2   |    18
2      |   name2    |   family2   |   NULL     |    NULL
NULL   |   NULL     |   NULL      |   order3   |    16

正如您在最后一行中看到的那样，它没有显示 Id 列。如何更改查询以返回最后一行中的 Id 列？我不想在我的选择查询中包含 table2.id 因为这样我将有两个 Id 列。

Answer 1

使用 COALESCE 或 ISNULL

COALESCE "returns the first non-null expression among its arguments," and ISNULL "replaces NULL with the specified replacement value."

http://sqlmag.com/t-sql/coalesce-vs-isnull 上的详分割析

SELECT ISNULL(table1.id, table2.id) AS id,
table1.name,table1.family,table2.orderr,table2.countt
FROM table1 FULL OUTER JOIN table2
ON table1.id = table2.id

或者

SELECT COALESCE(table1.id, table2.id) AS id,
table1.name,table1.family,table2.orderr,table2.countt
FROM table1 FULL OUTER JOIN table2
ON table1.id = table2.id