SQL每行一次插入到表2列

Question

I am stuck on a problem where I need to insert data into a another table, but in a way that I insert 2 columns, then stay on the same row, insert the next 2 and so on.

I have the following table data

I have a table with 2 columns I want to fill but want data to be entered like:

Row 1:(Row1A,Row1B)
Row 2:(Row1C,Row1D)
Row 3:(Row1E,Row1D)
Row 4:(Row2A,Row2B)
Row 5:(Row2C,Row2D)
Row 6:(Row2E,Row2F)

I can achieve the above using a loop, however I want to know another way that can improve performance. Is there a way to achieve this?

Edit: Order needs to be correct. I will need the first row columns added to the table first before moving onto second row.

Answer 1

I would use apply :

insert into t2(col1, col2)
    select col1, col2
    from data d cross apply
         (values (varchar1, varchar2), (varchar3, varchar4), (varchar5, varchar6)
         ) v(col1, col2);

Tables represent unordered sets. Because you have exactly two columns, you don't have a column to specify the ordering. If you did, then an order by would allow you to have an identity column that captures the ordering. This would look like:

insert into t2(col1, col2)
    select col1, col2
    from data d cross apply
         (values (varchar1, varchar2, 1), (varchar3, varchar4, 2), (varchar5, varchar6, 3)
         ) v(col1, col2, priority)
    order by d.id, v.priority;