Advantages and Disadvantages of High_Non_Group

Due to compression algorithms used, disk space requirements can be reduced without sacrificing performance.

If the column has a high number of unique values, this is the fastest index, with a few exceptions.

This index type is not recommended for GROUP BY queries.

Impossible if uniqueness is enforced.

You cannot use this index type if data in your columns is FLOAT, REAL, DOUBLE, BIT, BINARY, VARBINARY, CHAR > 255 bytes, or VARCHAR > 255 bytes.