Use of readpast may cause duplicates

Additional information is needed in the table describing isolation levels in the section “Using readpast” in the select description in Reference Manual Volume 2: Commands.

The additional information is for the line describing the 1, read committed line:

Using readpast may produce duplicates and adding the distinct clause will not clear this problem.

To resolve this, when using readpast, use a group by clause in addition to a distinct clause to avoid duplicates.