What is create MULTISET table in Teradata?
What is create MULTISET table in Teradata?
The purpose of MULTISET tables is to allow users to enter duplicate records. The presence the UNIQUE PRIMARY INDEX in a MULTISET table DDL is absolutely valid however it destroys the actual usage of MULTISET tables.
What is the difference between a set table and a MULTISET table in Teradata?
Set Versus Multiset Teradata classifies the tables as SET or MULTISET tables based on how the duplicate records are handled. A table defined as SET table doesn’t store the duplicate records, whereas the MULTISET table can store duplicate records.
What is derived table in Teradata?
Derived tables are an optional feature that you can specify in the FROM clause of SELECT, ABORT, ROLLBACK, and DELETE statements. You can use derived tables for these purposes: To avoid CREATE and DROP TABLE statements for storing retrieved information that is only needed for one request.
What are volatile tables in Teradata?
Volatile Table. Volatile tables are created, used and dropped within a user session. Their definition is not stored in data dictionary. They hold intermediate data of the query which is frequently used.
What is the difference between primary key and primary index in Teradata?
In Teradata ,Primary Key does not play as important role as Primary INDEX….5 differences between PRIMARY KEY and PRIMARY INDEX.
| # | PRIMARY KEY | PRIMARY INDEX |
|---|---|---|
| 1 | PRIMARY KEY cannot be NULL | PRIMARY INDEX can be NULL |
| 2 | PRIMARY KEY is not mandatory in Teradata | PRIMARY INDEX is mandatory in Teradata with exception of NOPI tables |
How will you create a table with select statement in Teradata?
CREATE TABLE active_employees AS ( SELECT * FROM employee e WHERE e.active_flg = ‘Y’ ) WITH DATA;
- Create a full copy of an existing table.
- Create a new copy of a table that contains only some of the original records – a subset.
- Create an empty table but with exactly the same structure of the original.
What is the difference between a permanent and temporary table Teradata?
Permanent storage of tables is necessary when different sessions and users must share table contents. When tables are required for only a single session, we can request the system to create temporary tables. When the session ends, the system automatically drops the temporary table.
What is on commit preserve rows in Teradata?
The ON COMMIT PRESERVE ROWS option provides the more normal situation where the table rows are kept after the end of the transaction. If the rows are going to be needed for other queries in other transactions.
What is the difference between a derived table and a subquery?
A subquery is a SELECT statement that is nested within another statement….Differences Among CTE, Derived Table, Temp Table, Sub Query And Temp Variable.
| Subquery | Derived |
|---|---|
| Subquery can have only one column. | Derived table can have one or more column. |
| Subquery mainly use in where clause. | Derived table used in from clause. |
What is a derived table?
A derived table is an expression that generates a table within the scope of a query FROM clause. For example, a subquery in a SELECT statement FROM clause is a derived table: SELECT … The number of column names must be the same as the number of table columns.
Why do we use volatile tables in Teradata?
Volatile tables do not have a persistent definition; they must be newly created each time you need to use them. Because volatile tables are private to the session that creates them, the system does not check their creation, access, modification, and drop privileges. …
Can you collect stats on volatile table?
Can I create statistics on a volatile table? Statistics are allowed, but when using the statement DIAGNOSTIC HELPSTAT ON FOR SESSION, we have to be aware that they are still proposed in the EXPLAIN plan. This is because they are not available to the optimizer in a DBC table.
How to create a multiset table in Teradata?
There are few differences between SET and MULTISET tables.Let’s discuss about syntax to create these tables. We have to specify the table type,table options,column definitions and Index definitions in the create table statement of Teradata.
How are string columns defined in Teradata table?
String columns VARCHAR & CHAR are defined as NOT CASESPECIFIC. First column is picked as PRIMARY INDEX if not explicitly mentioned in table definition and unique, primary key is also absent. Let’s create few more tables with some of the params for table/columns explicitly defined.
Which is the default format for a Teradata table?
Table is defined as FALLBACK so copy of the data is stored in another AMP. DATE columns have default format i.e. ‘YY/MM/DD’. String columns VARCHAR & CHAR are defined as NOT CASESPECIFIC. First column is picked as PRIMARY INDEX if not explicitly mentioned in table definition and unique, primary key is also absent.
Can a multiset table be created without an index?
MULTISET tables allow duplicate values in the table.We can create the MULTISET table without specifying the Index definitions such Primary Index or Unique Primary Index. By default,it allow the duplicate values if we not specifying index definitions.