What is primary index in Teradata?

Asked By: Prudencio Irigoyen | Last Updated: 26th May, 2020
Category: technology and computing data storage and warehousing
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Primary index is used to specify where the data resides in Teradata. It is used to specify which AMP gets the data row. Each table in Teradata is required to have a primary index defined. If the primary index is not defined, Teradata automatically assigns the primary index.

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Then, is primary index unique in Teradata?

Teradata Database Introduction to Teradata. You can create a table with a Unique Primary Index (UPI), a Non-Unique Primary Index (NUPI), or No Primary Index (NoPI). the PI is a column, or columns, that may have duplicate values. there is no PI column and rows are not hashed based on any column values.

Secondly, what is the difference between primary index and unique primary index in Teradata? Rule 5: The Primary Index of a populated table cannot be modified. Rule 6: A Primary Index has a limit of 64 columns. A Unique Primary Index (UPI) is unique and cannot have any duplicates. If you try and insert a row with a Primary Index value that is already in the table, the row will be rejected.

In this manner, what is primary and secondary index in Teradata?

A table can contain only one primary index. Teradata will perform full table scan for those queries. Secondary indexes resolve this issue. Secondary indexes are an alternate path to access the data. There are some differences between the primary index and the secondary index.

What is secondary index in Teradata?

A Secondary Index(SI) offers an alternative path to access the data. Unlike Primary Index which can only be defined at the time of table creation, a Secondary Index can be create/drop after the creation of the table also.

31 Related Question Answers Found

What is the difference between primary index and primary key?

Primary Key: that is used for uniquely identified a perticular row of a database table . Primary INDEX: That is used for getting a index from a database table and that indexing is done on unique based.

Can we create a table without primary index in Teradata?

You can create tables without a primary index (NoPI). The performance of FastLoad and Teradata Parallel Data Pump (TPump) Array INSERT operations can be enhanced by using NoPI staging tables. In all other circumstances, Teradata recommends that you specify a primary index when you create a table.

Does Teradata have primary key?

Teradata Database uses a unique primary or secondary index to enforce a primary key; therefore, the primary key can affect how Teradata Database distributes and retrieves rows. Although the primary key is often used as the primary index for a table, it may or may not be the best column set to choose as a primary index.

What is secondary index?

A secondary index, put simply, is a way to efficiently access records in a database (the primary) by means of some piece of information other than the usual (primary) key. Secondary indexes can be created manually by the application; there is no disadvantage, other than complexity, to doing so.

Does primary key imply unique?

Key Differences Between Primary key and Unique key:
A table can have only primary key whereas there can be multiple unique key on a table. A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.

How do you backup a table in Teradata?

CREATE TABLE active_employees AS ( SELECT * FROM employee e WHERE e.active_flg = 'Y' ) WITH DATA;
  1. Create a full copy of an existing table.
  2. Create a new copy of a table that contains only some of the original records - a subset.
  3. Create an empty table but with exactly the same structure of the original.

How do you select primary index in Teradata?

Use the following guidelines for selecting columns to be used as primary indexes:
  1. Select columns that consist mainly of unique, distinct values.
  2. Select columns that are most frequently used in equality predicate conditions.
  3. Select columns that are most frequently used to access rows.

How do I change primary index in Teradata?

In Teradata, we cannot alter a primary index once a table is created and the data is loaded into that table. So, to alter the primary index, we would need another copy of original table and then drop the actual table and recreate with required primary index.

What is difference between primary index and secondary index?

Primary IndexPrimary index is defined on an ordered data file. The data file is ordered on a key field. Secondary IndexSecondary index may be generated from a field which is a candidate key and has a unique value in every record, or a non-key with duplicate values.

What are join indexes in Teradata?

Join Index - Teradata. A Join Index is an index table that pre-joins the joined rows of two or more tables and, optionally, aggregates selected columns. They are used to speed up queries that frequently join certain tables. Teradata join indexes can be defined as hash-ordered or value-ordered.

Why nusi is all AMP operation?

NUSI access is always an all-AMPs operation unless the index is defined on the same columns as the primary index. This is allowed when the NUSI is value-ordered or when the table or join index is partitioned and not all the partitioning columns are included in the primary index.

How do I drop a secondary index in Teradata?

to drop unnamed secondary indexes, just reference the column combination, Syntax: drop index (emp_id,dept_id) ON happy_employees; Dropping a secondary index automatically drops the sub-tables and speeds up the data loads.

What is PPI in Teradata?

Partitioned Primary Index (PPI) is an indexing mechanism that is useful in improving the performance of certain queries. When rows are inserted into a table, they are stored in an AMP and arranged by their row hash order. When a table is defined with PPI, the rows are sorted by their partition number.

What is hash index in Teradata?

Hash index in Teradata has been designed to improve the performance of Teradata query in the way similar to the Single Table Join Index, which restricts parsing engine not to access or redistribute the base table. It may act like secondary index by providing an alternative access path for the base table.

What is unique index in Teradata?

Unique Indexes
A unique index column set, like a primary key column set constraint, enforces a unique value for that column set for each row in a table. USIs guarantee that each complete index value is unique, while ensuring that data access based on it is always at most a two-AMP operation.

What is Help stats in Teradata?

Help stats statement is used to view the collected statistics of a table in Teradata.

What is an index in db2 and types of indexes?

Db2 Index. Indexes are the database objects created based on one or more columns of a table. Indexes are used to improve the query performance and guarantee uniqueness when defined as unique indexes.