How to complete CONCAT if some of the values is missing - SQL?

Question

I'm very new in SQL and have to modify this existing code:

CONCAT(
    (SELECT value.string_value FROM UNNEST(event_params) WHERE key = 'series_title'), 
    ' : ',
    (SELECT value.string_value FROM UNNEST(event_params) WHERE key = 'episode_title')
  ) as complete_title,

My question is how to write if 'series_title' is missing?

I've put in this right before CONCAT, but it indicates that something is wrong/missing:

WHERE
  (SELECT value.string_value FROM UNNEST(event_params) WHERE key IS NULL)
  THEN
  (SELECT value.string_value FROM UNNEST(event_params) WHERE key = 'episode_title') as complete_title,
  ELSE

OK, some completions:

I have this query in BigQuery, which is NoSQL(?).

The reason of the modification is that the 'series_title' value, which we use to create the complete_title value, is missing for a part of our programs. So that I try to get pull out in these case is the 'episode_title' solely as complete_title . Otherwise - if both exist - 'series_title' and 'episode_title' together gets as complete_title .

event_params is the parameters we have available like this: enter image description here

Answer 1

我认为你想要NOT EXISTS ：

WHERE NOT EXISTS (SELECT 1 FROM UNNEST(event_params) WHERE key = 'series_title')