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The primary index contains key fields of a table and a pointer to non-key fields of the table. The primary index is created automatically when a table is created in database and moreover you can further define reference to the primary index which are known as Secondary index.
<b>Primary Key:</b>
This is an index that cannot be NULL, Primary Keys are used in building relationships between tables in a database. (an index is automatically created on the primary key). The difference between primary and ordinary keys is that there can be multiple keys, but only one primary key.
"The primary index is distinguished 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 primary index is created automatically when the table is created in the database."
please keep in mind that some DBMSs sort their main tables physically according to the primary key. Therefore searching via primary key is sometimes faster than searching via index (unique or not). (This is the performance forum after all, so this might be of interest to you).
Bluesky
