Introduction to Columnstore Indexes - Pro SQL Server Internals - page 712

Figure 34-19 shows the partial output of a query from Listing 34-12. Column 8, which does not have column
name displayed, represents the OrderId column, which is a part of the clustered index and has not been explicitly
defined in the columnstore index.
Figure 34-19. sys.column_store_segments output
The columns in the output represent the following:
column_id is the ID of a column in the index, which you can join with
the sys.index_columns view. As you have seen, only columns that are explicitly included
in an index have corresponding sys.index_columns rows.
partition_id references the partition to which a row group (and, therefore, a segment)
belongs. You can use it in a join with sys.partitions view to obtain object_id of the index.
segment_id is the ID of the segment, which is basically the ID of a row group. The first
segment in partition has ID of 0.
version represents a columnstore segment format. Both, SQL Server 2012 and 2014 return
1 as its value.
encoding_type represents the encoding used for this segment. It can have one of the
following four values:
Value-based encoding has encoding_type = 1
Dictionary encoding of non-strings has encoding_type = 2
Dictionary encoding of string values has encoding_type = 3
No encoding is used has encoding_type = 4
row_count represents number of rows in the segment.
has_null indicates if the data has null values.