Merge multiple rows with same ID into one row

Question

How can I merge multiple rows with same ID into one row.

When value in first and second row in the same column is the same or when there is value in fi

Answer 1

You can try something like this:

select 
isnull(t1.A, t2.A) as A,
isnull(t1.B, t2.B) as B,
isnull(t1.C, t2.C) as C
from
table_name t1
join table_name t2 on t1.ID = t2.ID and ..... 

You mention the concepts of first and second. How do
you define this order? Place that order defining condition
in here: .....

Also, I assume you have exactly 2 rows for each ID value.