Storage Structure of a Nested Structured Data Type - Teradata Database

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Storage Structure of a Nested Structured Data Type

A structured UDT can be built from attributes that are themselves structured UDTs. This topic explains the persistent storage format for a column having such a type.

The following graphic illustrates the basic morphology of a structured UDT that contains nested structured UDT attributes as it is stored in the row of a table in Teradata Database:



UDT element …

Specifies …

Typem ID

the TVMID type identifier for the level m structured UDT.

The value of m is 0 for the highest level attribute set in a structured UDT, ranging to 511 for the lowest possible level attribute set in a multilevel nested structured UDT.

Structured UDT attributes can be nested through multiple levels. The lowest level is numbered 511 because there can be 512 attribute nesting levels in a structured UDT, ranging from 0 - 511.

Presence Bits Arraym

the octet array of presence bits for the UDT at level m of the structured UDT.

This is a variably‑sized bit array, rounded to the higher modulo(8) boundary, whose size depends on the number of attributes stored for a particular structured UDT. Its size increases in octet (8‑bit byte) increments.

Attribute nm Value

attribute number n for the level m structured UDT component.

The number of attribute value columns is variable. The exact number depends on two factors:

  • The number of attributes a particular structured type has.
  • Whether or not an attribute is null.
  • The exact format of each attribute depends on the attribute type and is defined by the designer of the given structured type.