Guidelines for Using Multi-Value Compression
To change the values that are compressed or to change whether or not a column uses
compression, use an ALTER TABLE request. For example, the following turns off the
compression in the mycol_varchar column:
ALTER TABLE DB.mytable_vlc
ADD mycol_varchar NO COMPRESS;
You cannot compress more than 255 distinct values for an individual column.
You cannot create a table with more bytes compressed than there is room to store them
in the table header.
The maximum number of characters that can be listed in a COMPRESS clause is 8,188.
You cannot compress values in columns that are any of the following:
Primary index columns
Derived table columns
Derived period columns
Row‑level security constraint columns
Referenced primary key columns
Referencing foreign key columns for standard referential integrity relationships
You can compress values in referencing foreign key columns for Batch and Referential
Constraint referential integrity relationships.
You can compress columns that are a component of a secondary index, but MultiLoad
operations on a table with a secondary index can take longer if the secondary index
column set is compressed.
To avoid this problem, drop any compressed secondary indexes before starting the MultiLoad
job and then recreate them afterward.
You can compress columns that are components of a referential integrity relationship.
You can assign multi-value compression to columns that contain the following types
Nulls, including nulls for distinct and structured non‑LOB and non‑XML UDTs, ARRAY/VARRAY
and Period UDT data types
Constants having any of the data types supported by multi-value compression. See “Multi‑Value Compression” on page 699.