How do I convert given SQL query to SQL Server query?

Question

I have a SQL query I need to understand and translate to SQL Server query. Here is SQL query:

MERGE INTO study_event
    USING dual
    ON (study_id = :study_id)
       WHEN NOT MATCHED THEN
       INSERT (study_id, study_date)
       VALUES (:study_id, :study_date)

From how I understand, this means if study_event table doesn't have given study_id, I am inserting row to study_event table with given study_id and study_date. Is this correct?

I am trying to create SQL Server query that will do the same operation. From stack overflow, this is what I found:

INSERT INTO study_event(study_id, study_date)
SELECT x.*
FROM (VALUES(@study_id, @study_date)) as x(study_id, study_date)
WHERE NOT EXISTS (SELECT 1 FROM studies s1 WHERE s1.study_id = x.study_id)

I think I understand this query but I am not sure what SELECT x.* means. Would this query work and what does x.* mean?

Answer 1

x refers to the alias that the values() subquery creates, here:

FROM (VALUES(@study_id, @study_date)) as x(study_id, study_date)

This creates a derived table with one row and two columns study_id and study_date.

So basically x.* gives you the entire row from x, which contains the two original parameters to the query, @study_id and @study_date.

Disclaimer: I answered the original question!