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Can any one tell me what's the exact difference between Primary index & Secondary index? What are the different indexes that comes under category of primary & secondary index? And what's advantages of using primary index over secondary index & vice versa?
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The key field is generally the primary key of the relation. Secondary Index − Secondary 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. Clustering Index − Clustering index is defined on an ordered data file.
Indexes on Sequential files and Hash Tables are examples of primary indexes. Since a file can have at most one physical order then it can have at most one primary index. Secondary Indexes facilitate query-answering on attributes other than primary keys – or, more generally, on non-ordering attributes.
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.
The system distinguishes the primary index from the secondary indexes of a table. The primary index contains the key fields of the table and a pointer to the non-key fields of the table. The system creates the primary index automatically when the table is created in the database.
Primary index:
A primary index is an index on a set of fields that includes the unique primary key for the field and is guaranteed not to contain duplicates. Also Called a Clustered index. eg. Employee ID can be Example of it.
Secondary index:
A Secondary index is an index that is not a primary index and may have duplicates. eg. Employee name can be example of it. Because Employee name can have similar values.
The primary index contains the key fields of the table. The primary index is automatically created in the database when the table is activated. If a large table is frequently accessed such that it is not possible to apply primary index sorting, you should create secondary indexes for the table.
The indexes on a table have a three-character index ID. '0' is reserved for the primary index. Customers can create their own indexes on SAP tables; their IDs must begin with Y or Z.
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