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What is unique nonclustered constraint?
When you create a UNIQUE constraint, a unique nonclustered index is created to enforce a UNIQUE constraint by default. You can specify a unique clustered index if a clustered index on the table does not already exist.
Is unique key a constraint?
Unique key constraints can accept only one NULL value for column. Unique constraints are also referenced by the foreign key of another table….Comparison Chart:
| Parameter | PRIMARY KEY | UNIQUE KEY |
|---|---|---|
| Number of keys that can be defined in the table | Only one primary key | More than one unique key |
How do you remove a unique constraint?
To delete a unique constraint using Table Designer
- In Object Explorer, right-click the table with the unique constraint, and click Design.
- On the Table Designer menu, click Indexes/Keys.
- In the Indexes/Keys dialog box, select the unique key in the Selected Primary/Unique Key and Index list.
- Click Delete.
Why are I getting a primary / unique key violation?
Updating a row that causes a duplicate. This one is also fairly common. In this you are updating a row that causes a duplicate to occur. With the same result. Cannot insert duplicate key row in object ‘Person.Address’ with unique index ‘IX_Address_AddressLine1_AddressLine2_City_StateProvinceID_PostalCode’.
What to do if your primary key does not exist?
It most likely contain duplicates of the data that makes up your unique primary key. The where not exists does not protect against this because SQL is set based. You most likely need to either change the definition of your PK, change the content of the #StudentGrades table or change the select statement to give unique rows.
When do you get a duplicate key violation?
INSERT… (duplicate key violation). The only time conflicting locks will be taken is at the Insert stage. Then paste the below into two different SSMS windows. Take a note of the spids of the connections (x and y) and set up a SQL Profiler Trace capturing locking events and user error messages.
How to avoid insertion of duplicate key in SQL Server?
The second solution to avoid insertion of duplicate key is to execute an update or insert Secondly, the other solution is to update the table, then check the number of lines updated, if it equals zero, then no line is there and we can insert our line with 2000$ as sales amount using a classical INSERT statement.