如何在全外连接中合并select 2个同名参数

Question

我有 2 个 table 具有相同的 trial_id 字段名称。对于 full outer join，我想从每个单独的 table 中得到 trial_id。但我想将它合并为一个trial_id。我该怎么办？

SELECT ht.trial_id as trial_id, cts.trial_id AS trial_id, ht.subject, cts.trial_contract_name 
FROM
    hubspot_ticket ht 
FULL OUTER JOIN cs_trial_sheet cts 
        ON cts.trial_id = ht.trial_id

预期结果：只有一个 trial_id 列，并且不能为空。如果 ht.trial_id -> 得到 cts.trial_id.

Answer 1

select COALESCE(ht.trial_id, cts.trial_id) 作为 trial_id

Answer 2

可以根据MySQL的Join Documentation使用COALESCE():

The single result column that replaces two common columns is defined using the coalesce operation. That is, for two t1.a and t2.a the resulting single join column a is defined as a = COALESCE(t1.a, t2.a), where:

COALESCE(x, y) = (CASE WHEN x IS NOT NULL THEN x ELSE y END)

If the join operation is any other join, the result columns of the join consist of the concatenation of all columns of the joined tables.

试试这个：

select ht.subject, cts.trial_contract_name,
COALESCE(ht.trial_id, cts.trial_id) AS trial_id
FROM
    hubspot_ticket ht 
FULL OUTER JOIN cs_trial_sheet cts 
        ON cts.trial_id = ht.trial_id

但是，我不认为MySQL有FULL OUTER JOIN，我通常用LEFT JOIN、UNION、RIGHT JOIN作为替代。

如何在全外连接中合并select 2个同名参数

How to merge select 2 same name param in full outer join

sql

full-outer-join