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U
unbalanced hierarchy
A dimension hierarchy in which leaf nodes differ in their distances from the root node. Component part and organization chart hierarchies are usually unbalanced. See also ragged hierarchy.
underlying table
A table referenced by a view, cursor, or stored procedure. See also base table.
unenforced relationship
A link between tables that references the primary key in one table to a foreign key in another table and that does not check the referential integrity during INSERT and UPDATE transactions. An unenforced relationship is represented in a database diagram by a dashed line.
Unicode
Unicode defines a set of letters, numbers, and symbols that SQL Server recognizes in the nchar, nvarchar, and ntext data types. Unicode is related to but separate from character sets. Unicode has more than 65,000 possible values compared to a character set’s 256 and takes twice as much space to store. Unicode includes characters for most languages.
Unicode collation
This collation acts as a sort order for Unicode data. Unicode collation is a set of rules that determines how SQL Server compares, collates, and presents Unicode data in response to database queries.
Unicode format
Data that is stored in a bulk copy data file by using Unicode characters.
Union query
A query that combines two tables by performing the equivalent of appending one table onto the other.
UNIQUE constraints
Constraints that enforce entity integrity on a non-primary key. UNIQUE constraints ensure that no duplicate values are entered and that an index is created to enhance performance.
unique index
An index in which no two rows are permitted to have the same index value, thus prohibiting duplicate index or key values. The system checks for duplicate key values when the index is created and checks that each time data is added with an INSERT or UPDATE statement.
uniqueidentifier data type
A data type containing a unique identification number stored as a 16-byte binary string used for storing a globally unique identifier (GUID).
update
The act of modifying one or more data values in an existing row or rows (typically by using the UPDATE statement). Sometimes, the term update refers to any data modification (including insert, update, and delete operations).
update lock
A lock placed on resources (such as row, page, or table) that can be updated. Updated locks are used to prevent a common form of deadlock that occurs when multiple sessions are locking resources and are potentially updating them later.
Update query
A query that changes the values in columns of one or more rows in a table.
update statistics
A process that recalculates information about the distribution of key values in specified indexes. Query Optimizer uses these statistics to determine the most efficient way to execute a query.
user (account)
A SQL Server security account or identifier that represents a specific user in a database. Each user’s Windows account or SQL Server login is mapped to a user account in a database. Then, the appropriate permissions are granted to the user account. Each user account can only access data with which it has been granted permission to work.
user database
A database created by a SQL Server user and used to store application data. Most users connecting to instances of SQL Server reference user databases only, not system databases. See also system databases.
user-defined data type
A data type, based on a SQL Server data type, created by the user for custom data storage. Rules and defaults can be bound to user-defined data types (but not to system data types). See also base data type.
user-defined event
A type of message defined by a user that can be traced by SQL Profiler or used to fire a custom alert. Typically, the user is the system administrator.
user-defined function
In Analysis Services, a function defined in a Microsoft ActiveX library that is created by using a Component Object Model (COM) automation language such as Visual Basic or Visual C++. Such libraries can be registered with Analysis Services, and their functions can be called from multidimensional expressions (MDX) queries.In SQL Server, a Transact-SQL function defined by a user. Functions encapsulate frequently performed logic in a named entity that can be called by Transact-SQL statements instead of recoding the logic in each statement.
utility
A SQL Server application run from a command prompt to perform common tasks.
