The users are importing data from various external systems so ContactId will not be unique across the board but will be unique on a per user basis. I know how to create Unique and Non-Null contraints based on single columns but how can I create a unique contraints across 2 columns?
173 I have SQL Server 2008 R2 and I want to set a unique column. There seems to be two ways to do this: "unique index" and "unique constraint". They are not much different from what I understand, although unique constraint is recommended by most, because you also get an index automatically. How do I create a unique constraint?
I want to have a unique constraint on a column which I am going to populate with GUIDs. However, my data contains null values for this columns. How do I create the constraint that allows multiple n...
How do I create a unique constraint on a varchar field that is case sensitive (SQL Server 2005)? Currently my constraint looks like this: alter table MyTable add constraint UK_MyTable_MyUniqueKey
ALTER TABLE [dbo]. [tablename] DROP CONSTRAINT [unique key created by sql] GO alternatively: go to the keys -- right click on unique key and click on drop constraint in new sql editor window.
324 By using the constraint definition on table creation, you can specify one or multiple constraints that span multiple columns. The syntax, simplified from technet's documentation, is in the form of:
FROM sys.objects WHERE type_desc LIKE '%CONSTRAINT' AND OBJECT_NAME(OBJECT_ID)='XYZ' If you need even more constraint information, look inside the system stored procedure master.sys.sp_helpconstraint to see how to get certain information. To view the source code using SQL Server Management Studio get into the "Object Explorer".
The UNIQUE constraint uniquely identifies each record in a database table. The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns.
Now, a unique index and a unique constraint happen to be implemented the same way under the covers in SQL Server, so this is just semantics. But your documentation should explain why this is a constraint enforced via an index.
