Sql-Reference: Projection column encoding

Mon, 01 Jan 0001 00:00:00 +0000

After you create a table and its projections, you can call ALTER TABLE...ALTER COLUMN to set or change the encoding type of an existing column in one or more projections. For example:

ALTER TABLE store.store_dimension ALTER COLUMN store_region
  ENCODING rle PROJECTIONS (store.store_dimension_p1_b0, store.store_dimension_p2);

In this example, the ALTER TABLE statement specifies to set RLE encoding on column store_region for two projections: store_dimension_p1_b0 and store_dimension_p2. The PROJECTIONS list references the two projections by their projection name and base name, respectively. You can reference a projection either way; in both cases, the change is propagated to all buddies of the projection and stored in its DDL accordingly:

=> select export_objects('','store.store_dimension');

                          export_objects
------------------------------------------------------------------
CREATE TABLE store.store_dimension
(
    store_key int NOT NULL,
    store_name varchar(64),
    store_number int,
    store_address varchar(256),
    store_city varchar(64),
    store_state char(2),
    store_region varchar(64)
);

CREATE PROJECTION store.store_dimension_p1
(
 store_key,
 store_name,
 store_number,
 store_address,
 store_city,
 store_state,
 store_region ENCODING RLE
)
AS
 SELECT store_dimension.store_key,
        store_dimension.store_name,
        store_dimension.store_number,
        store_dimension.store_address,
        store_dimension.store_city,
        store_dimension.store_state,
        store_dimension.store_region
 FROM store.store_dimension
 ORDER BY store_dimension.store_key
SEGMENTED BY hash(store_dimension.store_key) ALL NODES KSAFE 1;

CREATE PROJECTION store.store_dimension_p2
(
 store_key,
 store_name,
 store_number,
 store_address,
 store_city,
 store_state,
 store_region ENCODING RLE
)
AS
 SELECT ...

Important

When you add or change a column's encoding type, it has no immediate effect on existing projection data. OpenText™ Analytics Database applies the encoding only to newly loaded data, and to existing data on mergeout.

OpenText Analytics Database 26.2.x – ALTER TABLE

Sql-Reference: Projection column encoding

Important