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25 Σεπ 2010 · Unique Key: It is a constraint which imposes limitation on database. That limitation is it will not allow duplicate values . For example if you want to select one column as primary key it should be NOT NULL & UNIQUE. Unique Index: It is a index which improves the performance while executing queries on your data base. In unique index it also not ...
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.
5 Μαΐ 2023 · This topic describes how to create a unique index on a table in SQL Server by using SQL Server Management Studio or Transact-SQL. A unique index guarantees that the index key contains no duplicate values and therefore every row in the table is in some way unique.
23 Μαρ 2019 · However, if we attempt to insert a duplicate key into a unique index that was created with the WITH IGNORE_DUP_KEY clause, SQL Server merely discards the "bad" row, generates a warning message, and continues executing the remainder of the statement. Note that SQL Server only generates the warning for actual insert statements.
9 Δεκ 2022 · You can get the proper ANSI behavior in SQL Server 2008 and above by creating a unique, filtered index. CREATE UNIQUE INDEX foo ON dbo.bar(key) WHERE key IS NOT NULL; This allows more than one NULL value because those rows are completely left out of the duplicate checking.
29 Δεκ 2009 · I then clean the database of the duplicated, recreated the index with the same 3 varchars as unique and nonclustered and now it works properly, not allowing duplicates. Does anyone know why the uniqueness of this index was ignored?
1 Φεβ 2012 · Declaring a PRIMARY KEY or UNIQUE constraint causes SQL Server to automatically create an index. You can have a unique index without having a matching constraint; but you cannot have either of...
