Which index type is defined when a table is created?

The primary index is defined when a table is created in Teradata. It serves as the main mechanism for data distribution across the nodes of the Teradata system, meaning it determines how data is stored and accessed within the database. Each table must have a primary index, which can be either unique or non-unique, and it plays a crucial role in how Teradata organizes data to optimize performance.

By creating a primary index during the table creation process, Teradata ensures efficient access to the data, as the primary index helps to quickly locate the rows based on their unique identifiers (the value stored in the primary index). It also guarantees that each row will have a defined location in storage, which is essential for high-speed processing and retrieval of records.

In contrast, secondary indexes, join indexes, and unique indexes are not mandatory at the time of table creation. They can be added later to support specific queries or improve performance for certain operations, but the primary index is foundational and must be established upfront as part of the table definition. This is why the primary index is the correct choice for this question.