SQL Index

• Indexes are special lookup tables used to retrieve data from the database very quickly.
• An index is used to speed up SELECT queries and WHERE clauses. However, it may slow down data input operations like INSERT and UPDATE.
• Indexes can be created or dropped without affecting the data in the database.
• An index in a database is similar to an index in the back of a book—it helps you locate information quickly.

Creating an Index

You can create an index using the CREATE INDEX statement.

Syntax

CREATE INDEX index_name
ON table_name (column1, column2, ...);
 
# Unique Index in SQL
 
A **Unique Index** ensures that the values in the indexed columns are unique.
 
## Syntax
 
```sql
CREATE UNIQUE INDEX index_name
ON table_name (column1, column2, ...);