Secondary Index In TeraData

Secondary Index

Real time usage

Other than primary index columns if we are using in the where clause, To get fast retrieval data take second index on the columns.

Features

It prevents full table scan

Basically for getting fast Retrieval of data, this is record mended

We can create and drop SI at any time (Creation can be at table creation/after table creation)

We can create Max 32, SI, a size in single table.

USI takes only unique value

NSUI takes duplicate and nulls

For range based data VOSI is useful

It doesn’t effect data distribution.

It uses a sub table mechanism as part of its operations

Each SI can be composite till 64 columns

It is two or many Amp operation.

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S.I Sub table Mechanism[Storage and retrieval Architecture]

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Sel* from party where pcode=20;

Party

PID	PNM	PCODE
1	X	100
2	Y	20
3	Z	33
4	K	20

Sub table content added and remove according to the main table content, which is burden to system

Sub table may in the same Amp(or) it may be indifferent Amp

S.I ROW ID	Column value	P.I row ID
	202033100

Sel * from party where P Code between 20 and 33

Note

In case of USI Sub table will be in other Amp

In case of NUSI Sub table will be in the same Amp.

Creation and dropping

AT table creation

USI:_ Create table<table name>unique index(column name)

NUSI:- Create table<table name> index(column name)

After table creation

USI:_ Create unique index idx- party CD(party code) on party;

NUSI:- Create index idx- party CD(party code) on party

Value order NUSI

Create index (party code) order by values on party;

Dropping indexes

Named index dropping:_ Drop index<index name>on<table name>

Unnamed index dropping:_ Drop index(Column name)on<table name>

Final Example

Create set table party test fall back (party id integer, party name varchar(30)upper case, party income integer check(party income>5000), party code integer) unique primary index(party id)unique index(party code)

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Difference between PI and SI

FAQ’S

There is table with primary key and unique key is available what types of index the system create by default?

Ans:- As primary key give high priority , it takes UPI on primary key and USI on unique

a) UPI:- UPI on primary key column and unique key column as USI

b)USI:- USI on unique key column

Learn more about Teradata Interview Questions in this blog post.

Naming conversion And rules

a) As per BIET Names are limited to 30^th character

b) A name can be combination of A-Z, a-Z,$,#,-

c) Object Name is unique in tera data

USI

Takes unique values, generally sub table stoves in other Amp’s

[Two Amp operations and returns only one row]

VOSI - In this situation instated of secondary index row ID/row hash sequence actual values will be order so that this index is useful for range based query operations.

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