Changing column groups
Warning
Supported only for row-oriented tables. Support for column-oriented tables is currently under development.
The mechanism of column groups allows for improved performance of partial row read operations by dividing the storage of table columns into several groups. The most commonly used scenario is to organize the storage of infrequently used attributes into a separate column group.
Creating column groups
ADD FAMILY
: Creates a new group of columns in the table. The code below creates the family_small
column group in the series_with_families
table.
ALTER TABLE series_with_families ADD FAMILY family_small (
DATA = "ssd",
COMPRESSION = "off"
);
Modifying column groups
Using the ALTER COLUMN
command, you can change a column group for the specified column. The code below for the release_date
column in the series_with_families
table changes the column group to family_small
.
ALTER TABLE series_with_families ALTER COLUMN release_date SET FAMILY family_small;
The two previous commands from listings 8 and 9 can be combined into one ALTER TABLE
call. The code below creates the family_small
column group and sets it for the release_date
column in the series_with_families
table.
ALTER TABLE series_with_families
ADD FAMILY family_small (
DATA = "ssd",
COMPRESSION = "off"
),
ALTER COLUMN release_date SET FAMILY family_small;
Using the ALTER FAMILY
command, you can change the parameters of the column group. The code below changes the storage type to hdd
for the default
column group in the series_with_families
table:
ALTER TABLE series_with_families ALTER FAMILY default SET DATA "hdd";
Note
Available types of storage devices depend on the YDB cluster configuration.
You can specify any parameters of a group of columns from the CREATE TABLE
command.