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:
where:
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UDT element … |
Specifies … |
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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. |
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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. |
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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 exact format of each attribute depends on the attribute type and is defined by the designer of the given structured type. |