Teradata - Primary Index
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. Primary index provides the fastest way to access the data. A primary may have a maximum of 64 columns.
Primary index is defined while creating a table. There are 2 types of Primary Indexes.
- Unique Primary Index(UPI)
- Non Unique Primary Index(NUPI)
Unique Primary Index (UPI)
If the table is defined to be having UPI, then the column deemed as UPI should not have any duplicate values. If any duplicate values are inserted, they will be rejected.
Create Unique Primary Index
The following example creates the Salary table with column EmployeeNo as Unique Primary Index.
CREATE SET TABLE Salary ( EmployeeNo INTEGER, Gross INTEGER, Deduction INTEGER, NetPay INTEGER ) UNIQUE PRIMARY INDEX(EmployeeNo);
Non Unique Primary Index (NUPI)
If the table is defined to be having NUPI, then the column deemed as UPI can accept duplicate values.
Create Non Unique Primary Index
The following example creates the employee accounts table with column EmployeeNo as Non Unique Primary Index. EmployeeNo is defined as Non Unique Primary Index since an employee can have multiple accounts in the table; one for salary account and another one for reimbursement account.
CREATE SET TABLE Employee _Accounts ( EmployeeNo INTEGER, employee_bank_account_type BYTEINT. employee_bank_account_number INTEGER, employee_bank_name VARCHAR(30), employee_bank_city VARCHAR(30) ) PRIMARY INDEX(EmployeeNo);