SQL条件连接列 [英] SQL Conditional JOIN column

问题描述

我想根据当前行的值确定JOIN列.

I want to determine the JOIN column based on the value of the current row.

例如，我的工作表有4个日期列:offer_date，accepted_date，start_date，reported_date.

So for example, my job table has 4 date columns: offer_date, accepted_date, start_date, reported_date.

我想根据日期检查汇率.我知道reported_date永远不会为空，但这是我的最后选择，因此我有一个优先顺序要加入到exchange_rate表中.我不确定如何使用CASE语句执行此操作，即使那是正确的方法.

I want to check against an exchange rate based on the date. I know the reported_date is never null, but it's my last resort, so I have a priority order for which to join against the exchange_rate table. I'm not quite sure how to do this with a CASE statement, if that's even the right approach.

INNER JOIN exchange_rate c1 ON c1.date = {{conditionally pick a column here}}

  -- use j.offer_date if not null
  -- use j.accepted_date if above is null
  -- use j.start_date if above two are null
  -- use j.reported_date if above three are null

推荐答案

尝试这样的逻辑:

INNER JOIN
exchange_rate c1
ON c1.date = coalesce(j.offer_date, j.accepted_date, j.start_date, j.reported_date)

coalesce()函数返回列表中的第一个非NULL值.

The coalesce() function returns the first non-NULL value in the list.

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