I had always understood that SQL Server auto-created statistics only include one column. In other words, they are not multi-column statistics.
However, today I came across some auto-created statistics that have two columns. The second column is always the primary key of the table. There are other auto-created statistics on the same table that don't have a second column.
auto_created = 1 on the sys.stats table.
Also, some statistics have a different naming convention on the exact same tables. Some of them have a column name in the statistic name. What makes SQL use a different naming convention? For example,
These are not causing problems, I am just curious about it.