1
vote
0answers
58 views

How to merge rows based on how much data they have?

I am cleaning data and I formed a table something like this: file | product | color | product_id --------------------------------------------- one.csv pipe blue null ...
-1
votes
2answers
180 views

Information sources for multiple hierachy trees in a single table

I need some quality sources - books, websites etc. - to educate myself about putting multiple hierarchy trees in a single table using SQL. I'm looking for some good theoretical and practical ...
7
votes
3answers
3k views

Why are NULLs sorted first?

Why is it that when we have a NULL value in a column and we order by the value ascending, the NULLs are sorted first? select 1 as test union all select 2 union all select NULL union all select 3 ...