SQL：按空列数排序

Question

I have a SQL query which displays a list of results. Every row in my database has about 20 columns and not every column is mandatory. I would like the result of the SQL query to be sorted by the number of filled in columns. The rows with the least empty columns at the top, the ones with the most empty columns at the bottom. Do any of you guys have an idea how to do this?

I thought about adding an extra column to the table which if updated every time the user edits their row, this number would indicate the number of empty columns and I could sort my list with that. This however, sounds like unnecessary troubles, but maybe there is no other way? I'm sure somebody on here will know!

Thanks,

Sander

Answer 1

You can do it in just about any database with a giant case statement:

order by ((case when col1 is not null then 1 else 0 end) +
          (case when col2 is not null then 1 else 0 end) +
          . . .
          (case when col20 is not null then 1 else 0 end)
         ) desc

Answer 2

You could order by the amount of empty columns:

order by
        case when col1 is null then 1 else 0 end + 
        case when col2 is null then 1 else 0 end +
        case when col3 is null then 1 else 0 end +
        ...
        case when col20 is null then 1 else 0 end

(Note the + at the end of the lines: it's only one column with the integer count of empty fields, sorted in ascending order.)