3
votes
1answer
72 views

What does the “structured” in Structured Query Language mean?

What makes SQL "structured"? Are structured query languages distinguishable from unstructured ones? And when we say that SQL is "declarative", is that a related concept?
1
vote
0answers
45 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
158 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 ...
5
votes
3answers
2k 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 ...