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Views in Teradata
12 October, 2020
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Views
- There are windows to tables, A view nothing but a logical collection of an attribute from the table on tables, we use views mainly for
- Taking requires rows and columns from the tables
- Reduce net bond width
- Providing better binding between table and view data
- Providing security on the table etc.
- Based on the functionality, there are 3 types of views
1. Read-only view
2. Updatable view
3. Materialize view
Materialize View
- This concept not available in Teradata, but we can implements through aggregate, join index (or) Global temporary tables
- In this view, it will have storage for view and it stores the calculated data.
- This storage and calculate data are useful to retrieve the data FASTER
- Generally, we go for a materialized view at the time of frequent analytical and AGGREGATE operations.
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Materialized View & Updatable view
If you create a view based on a single table, then it will be an updatable view here we can perform INSERT UPDATE And DELETE operations on views so that table will be effected
Create view VW party2 As(Select* From party)
Show view var _party2
Select* From VW-Party2
Replace view vw- Party2 As(Select party id, party name, party income from the party)
update vw- party2 set party income=7777 where party id=1
Read-only view(Join view and AGGREGATE View): Here we can perform any operations.
Join Views
Create view vw- party3 As(Select P. party id, t. party name from party p
Left after joining test t On p. party id=party id);
Show view vw- party3
Select* from vw- party3
Replacing view vw- party3 As(Select t. party name from party p Left after joining test t on p. party id= t. party id);
Aggregate Views
Aggregate Views are Views which contain Aggregate expressions or derived columns it is always necessary to assign a name to there columns so that they may be referenced within the view
An Optional Locking
Access clause may be added to the query which permits the table row to be read even in the event that another read or write lock is held on the table
Create view party sales as
Locking table party for access
Select party code as department
Sum(party income) As salary- total
Avg(Party income) As salary- Average
max(Party income) As salary- max
min (Party income) As salary- min
From party
Group by party code
Views with Check Option
The with check option prevents rows from being inserted (or) updated via the view if the resulting rows fall outside the view
Create view dept – budget as
Select party id party name from the party
Where party income<=100000 WITH CHEQ option;
Select *from party
Insert into dept – budget(party id, party income)values(603,700000);
*Failure 3564 Range constraint CHECK Error in field party name Department party income, Inserted or updated view this view may not exceed $ 1,00,000.
Restrictions on Views
An INDEX Cannot be created on a view
A view cannot contain an ORDER BY CLAUSE
Derived and aggregate column must be assigned as the name
A view cannot use for update operations if it contains:
Data from more than one table(i.e. Join views)
The same column specified twice
Derived columns(i.e Salary- Account/12)
A DISTINCT CLAUSE
A Group by CLAUSE
Note
The view contains only one select statement, view returns the result set
Difference MACROS And PROCEDURES
| Macros | Procedures |
| Collection of statements for implementing simple TASKS | Precompiled collection of statements for implementing compile TASKS Ex: a. Error Handling b. Working with multiple DML statements c. Knowing memory requirement etc.. |
| In real-time for simple and frequent required we go for macro | For rare request and complex operations, we go for in real-time |
| Runs at client side | Runs at server side |
| Execution results are cached so it gives faster response | Always runs at server side |
| Takes only i/p parameter | It takes
|
| All statements inside MARCO executed like a transaction | Not applicable |
| Security less | Security high |
| Network bandwidth less | More bandwidth |
| We can not execute procedure control statement [loops, If, while…] | Supports |
| It supports a maximum of one DDL statement | Procedure no limit |
| This is a reference by using “exec” (or) “execute” command | These are reference by using call common |
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