Is Oracle's primary key an index?

Oracle’s primary key is not an index; the primary key is one or more fields in the table. The value of the primary key is used to represent a record in the table, and there can only be one primary key. The index is a kind of function for the server to use. The database structure for quickly searching a row in a table is to speed up access to data in the table, and a table can have multiple indexes, so the primary key is not an index.

The operating environment of this tutorial: Windows 10 system, Oracle version 12c, Dell G3 computer.

Is Oracle’s primary key an index?

Primary key:

The field that uniquely identifies a record is the primary key (or primary code) and cannot be repeated Yes, it is not allowed to be empty.

Function: Used to ensure data integrity

Number: There can only be one primary key

The primary key (primary key) is one or more fields in the table. The value is used to uniquely identify a record in the table.

The so-called composite primary key means that the primary key of your table contains more than one field.

If there is no unique primary key in the table, you can use a composite primary key to determine the uniqueness of a record.

Index:

Function: To improve the speed of query sorting

Number: A table can have multiple indexes

In Oracle, an index is a database structure that allows the server to quickly find a row in a table.

An index is an auxiliary object built on one or more columns of a table to speed up access to data in the table.

The structure of oracle storage index is B* number (balanced tree), and the index is composed of root node, branch point and leaf point. The upper-level index block contains the index data of the lower-level index block, and the leaf node contains the index data. and the rowid that determines the actual location of the row.

Creating indexes in the database mainly has the following functions:

(1) Quickly access data.

(2) Reduce I/O operations

(3) It can not only improve database performance, but also ensure the uniqueness of column values.

(4) Implement referential integrity between tables

(5) When using orderby and groupby clauses for data retrieval, using indexes can reduce the time of sorting and grouping.

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