What is the difference between clustered and non-clustered indexes in SQL?

Clustered Index

Non-Clustered Index

A clustered index is a table or view where the data for the rows are stored. In a relational database, if the table column contains a primary key, MySQL automatically creates a clustered index named PRIMARY.

The indexes other than PRIMARY indexes (clustered indexes) are called non-clustered indexes. It has a structure separate from the data row. The non-clustered indexes are also known as secondary indexes.

Clustered indexes store the data information and the data itself.

Non-clustered indexes stores only the information, and then it will refer you to the data stored in clustered data.

There can only be one clustered index per table.

There can be one or more non-clustered indexes in a table.

A clustered index determines how data is stored physically in the table. Therefore, reading from a clustered index is faster.

It creates a logical ordering of data rows and uses pointers for accessing the physical data files. Therefore, reading from a clustered index is slower.

A clustered index always contains an index id of 0.

A non-clustered index always contains an index id>0.