What is the difference between index and unique index?

What is the difference between index and unique key?

There is no difference between Unique Index and Unique Constraint. Even though syntax are different the effect is the same. Unique Constraint creates Unique Index to maintain the constraint to prevent duplicate keys.

What is indexes difference between unique and non unique indexes?

In addition to enforcing the uniqueness of data values, a unique index can also be used to improve data retrieval performance during query processing. Non-unique indexes are not used to enforce constraints on the tables with which they are associated.

Is index the same as unique constraint?

Conclusion. Generally there is no functional difference between a unique index and a unique constraint. The latter is also listed as a constraint, however this is only a method to emphasize the purpose of the index.

What is a unique index SQL?

SQL Server unique index overview A unique index ensures the index key columns do not contain any duplicate values. A unique index may consist of one or many columns. If a unique index has one column, the values in this column will be unique.