SQL Joins

I've never used SQL joins frequently enough to remember which one is which, and end up looking them up. This visual explanation of joins using Venn diagrams is a great quick reference.  The examples don't include duplicate in the tables, and it doesn't have a visual representation of a cross join a natural join or a self join.

Concatenate rows into a text string

I needed to concatenate multiple rows of a table together in Caché SQL. I did this using XMLAGG, which returns all of the values used within a specified column as a concatenated string.  If I'd wanted the data to be comma separated then I could have used the LIST function instead.

SELECT ReportName,XMLAGG(ReportLine) As Report FROM Reports GROUP BY ReportName

If you want to do the same thing with a different database then Stack Overflow thread might be able to help.