What is a clustered index?
A clustered index is a type of index in which the table records are physically rearranged to match the index.
Clustered indexes are effective on columns that are searched for a range of values. After the row with the first value is found using a clustered index, rows with subsequent index values are guaranteed to be physically adjacent, allowing faster access for a user query or application.
In other words, a clustered index stores the actual data, and a non-clustered index is a pointer to the data. In most DBMS, you can only have one clustered index per table, although there are systems that support multiple clusters (DB2 is an example).
As with a regular index that is stored unsorted in a database table, a clustered index can be a composite index; B. a concatenation of first and last name in a table with personal information.