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]
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)
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
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Naming conversion And rules
- a) As per BIET Names are limited to 30th 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.
Characters literal and Numeric literal
General we used select, insert etc statement
Select
Party id,
Party name,
‘IT’ as deptCharacter Literal
40 as code Numeric literal
From party;
| Party id | Party name | dept | Code |
| 1 | Vinay | IT | 40 |
| 2. | Madhu | IT | 40 |
| 3. | Meera | IT | 40 |
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