In SQL, index, and key both are different. Even though both look the same In fact, both works differently in RDBMS of any relational database. The index is one kind of relational database object, whereas Key is different and it maintains the relation between different tables. Explained in my previous post about features of RDBMS
Differences between Index and Key.
The benefits of Index are
- To improve query performance. Indexes can be used to access the data faster using direct access to rows based on the index key values.
- To guarantee uniqueness when they are defined as unique indexes
A Key can be single or multiple columns of a table. You can find different keys available in relational database
The benefits of Key
- Keys are important in a relational database because they ensure that each record in a table is uniquely identified, they help establish and enforce referential integrity, and they establish relationships between tables.
- The same column can be part of more than one key
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