17.10 - Rules for Partition Formats in a Column-Partitioned Table - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQL Data Definition Language Detailed Topics

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Release Date
July 2021
Content Type
Programming Reference
Publication ID
B035-1184-171K
Language
English (United States)
  • If you specify COLUMN format for a column partition, Vantage stores 1 or more column partition values in a physical container.

    A column partition value consists of the values of the columns contained in the column partition.

  • The following rule applies to autocompression for a column partitioning level.
    Autocompression Option or Default Column Partitioning Level Override Setting for Partition
    COLUMN AUTO COMPRESS NO AUTO COMPRESS.
    COLUMN NO AUTO COMPRESS AUTO COMPRESS.
  • If you specify COLUMN without also specifying AUTO COMPRESS or NO AUTO COMPRESS for a column partitioning level, Vantage assigns AUTO COMPRESS for the partitioning level.
  • If you specify ROW format for a column partition, Vantage stores only 1 column partition value in a physical subrow.

    A subrow is a standard Teradata row format, and the term is used to emphasize that it is part of a column partitioning.

  • If you specify a column or constraint grouping or both with COLUMN format in the column list, the grouping defines a column partition and Vantage stores 1 or more column partition values in a physical container using COLUMN format.

    If you specify a column or constraint grouping or both with ROW format in the column list, the grouping defines a column partition that stores only 1 column partition value in a physical subrow using ROW format.

    If you specify neither COLUMN nor ROW format for a column or constraint grouping, the grouping defines a column partition and Vantage determines whether to use a COLUMN or ROW format for that column partition.

  • If you do not specify an explicit COLUMN or ROW format for a partition, Vantage makes the determination for you implicitly.

    When the COLUMN or ROW format is system-determined, Vantage bases its choice of format on the size of a column partition value for the column partition and other factors such as whether a column partition value for the column partition has fixed or variable length and whether the column partition is a single-column or multicolumn partition.

    Vantage generally assigns a COLUMN format to a narrow column partition and assigns a ROW format to a wide column partition. In this context, a column partition is considered to be narrow when its size is roughly 256 or fewer bytes.

    The width of a variable length column in a column partition is estimated as


    Variable column width in column partition equation

    You can submit a HELP COLUMN statement or select the ColumnPartitionFormat column from the DBC.ColumnsV(X) view to determine which format Vantage elected to use for a column partition.