Indexes and Keys (197)

Although the terms are often used interchangeably, indexes and keys are different.
Indexes are structures actually stored in the database, which users create, alter, and
drop using SQL statements. You create an index to provide a fast access path to table
data. Keys are strictly a logical concept. Keys correspond to another feature of Oracle
called integrity constraints, which enforce the business rules of a database.

Because Oracle uses indexes to enforce some integrity constraints, the terms key and
index are often are used interchangeably. However, do not confuse them with each
other.

索引與鍵
1. 索引是在資料庫中實際儲存的資料結構,使用者可以使用 SQL 語句對其進行建立,修改,或移除.
索引提供了一種快速訪問表資料的途徑.
2. 鍵只是一個邏輯概念.鍵的概念主要在 Oracle 的完整性約束功能中使用.

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