- To change the values that are compressed or to change whether 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 can be stored 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
- Identity 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.Referential integrity is supported only on the Block File System on the primary cluster, not on the Object File System.
- 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 those indexes afterward.
- You can compress columns that are components of a referential integrity relationship.
- You can assign multivalue compression to columns that contain the following types of data:
- Nulls
- Zeros
- Blanks
- Constants having any of the data types supported by multivalue compression.