Selecting both MIN and MAX From the Table is slower than expected

Question

I have a table MYTABLE with a date column SDATE which is the primary key of the table and has a unique index on it.

When I run this query:

Answer 1

The Index Full Scan can only visit one side of the index. When you are doing

SELECT MIN(SDATE), MAX(SDATE) FROM MYTABLE

you are requesting to visit 2 sides. Therefore, if you want both the minimum and the maximum column value, an Index Full Scan is not viable.

A more detailed analyze you can find here.