Glosario de Bases de Datos Sybase, "S"

See System Administrator .

See search argument  

A marker that the user puts inside a user-defined transaction. The user can later use the rollback transaction command with the savepoint name to cancel any commands up to the savepoint, or commit transaction to actually complete the commands. See also transaction and rollback transaction .

An aggregate function that produces a single value from a select statement that does not include a group by clause. This is true whether the aggregate function is operating on all the rows in a table or on a subset of rows defined by a where clause. See also vector aggregate.

The maximum number of digits that can be stored to the right of the decimal point by a numeric or decimal datatype. The scale must be less than or equal to the precision .

An internal data structure that manages the scan of tables being queried, particularly tables that have references to other tables.

A collection of objects associated with a particular schema name and schema authorization identifier . The objects can be tables, views, domains, constraints, assertions, privileges, and so on. A schema is created by a create schema statement.

All the objects are said to be owned by or to have been created by the associated schema authorization identifier for the schema.

The context in which a feature, such as a cursor or a global variable , is used. In Adaptive Server, the scope can be an individual user session, a stored procedure , or a trigger .

A predicate in a query's where clause that can be used to locate rows via an index. Also referred to as SARG.

A named subset of database devices available to a particular database. It is a label that points to one or more database devices. Segments can be used to control the placement of tables and indexes on specific database devices.

The column s specified in the main clause of a select statement. In a dependent view, the target list must be maintained in all underlying views if the dependent view is to remain valid.

A subset of the row s in a table. Also called a restriction, it is one of the basic query operations in a relational system. See also producer process and view .

See index selectivity and join selectivity .

A join used for comparing values within a column of a table . Since this operation involves a join of a table with itself, you must give the table two temporary names, or correlation names , which are then used to qualify the column names in the rest of the query.

A semaphore is a simple internal locking mechanism that prevents a second task from accessing the data structure currently in use. Adaptive Server uses semaphores to protect transaction logs, user log caches, and I/O devices. Like a spinlock , a semaphore is relevant only in SMP environments.

An interface specification defining remote access for use with Component Integration Services. For each server class there is a separate access method that handles interaction between the server and remote servers of the same class. Each server class has a set of unique characteristics that System Administrators and programmers use to configure the server for remote data access. The characteristics are:

• Mapping between local tables (proxy tables) and external objects
• Datatype conversions specific to the class or access method
• Special considerations for each class
• Restrictions, if any, on Transact-SQL statements applied to the class

A cursor declared inside a stored procedure . The client executing the stored procedure is not aware of the presence of these cursors. Results returned to the client for a fetch appear exactly the same as the results from a normal select.

See engine .

The ID number by which a user is known to Adaptive Server.

The severity of an error condition.

A type of lock acquired on an object for a read operation. It does not allow other transactions to acquire exclusive locks on the object but allows them to acquire shared locks. Shared locks can be obtained on a table or page.

A corruption in Adaptive Server that is usually not persistent. Most soft faults result from temporary inconsistencies in the target database caused by users updating the target database during the dbcc checkstorage operation or by dbcc checkstorage encountering Data Definition Language (DDL) commands. These faults are not repeated when you run dbcc checkstorage a second time. See also hard fault .

A specification used by Adaptive Server to determine the order in which to sort character data. Also called collating sequence.

SQL statements that define a compiled object. Source text is stored in the text column of the syscomments table. It is used during upgrade processes; therefore, it must not be deleted. Source text can be encrypted using sp_hidetext.

A simple internal locking mechanism that prevents a process from accessing the resource currently used by another process. All processes trying to access the resource must wait (or "spin") until the lock is released. Spinlocks protect internal data structures such as a data cache.

See Structured Query Language (SQL)

See Adaptive Server .

One or more complete Transact-SQL command s. A statement usually consists of a keyword , for example, select, followed by clauses such as from or where  

A series of Transact-SQL statement s enclosed between the keyword s and end so that they are treated as a unit.

A collection of Transact-SQL statement s and optional control-of-flow statements stored under a name. See also system procedure .

A function that operates on strings of characters or binary data. substring and charindex are Transact-SQL string functions.

The language used to communicate with a relational database and that is the subject of standards set by several standards bodies.

A server process acting on behalf of a user. In Adaptive Server, subjects include users, and stored procedure s and trusted trigger s while executing.

A select statement that is nested inside another select, insert, update , or delete statement or inside another subquery.

A page that recovery has marked as suspect because of corruption. Suspect pages are normally inaccessible to users unless they have been forced online by special procedures.

An environment in which multiple CPUs simultaneously process client tasks. Any CPU can execute any task.

An assortment of tasks including but not limited to managing Adaptive Server's physical storage, creating and backing up databases, creating user accounts, granting permissions, and running diagnostic and repair functions. See also database administration .

A user in charge of Adaptive Server system administration, including managing disk storage, granting and revoking the System Administrator role, and creating new databases. The "sa" account, a single login , is created when Adaptive Server is installed. This login is configured with both the System Administrator and System Security Officer roles. To increase individual accountability, use the "sa" account to assign roles to individual logins.

A database provided Sybase, for example, master, tempdb, model, and sybsystemprocs.

A function that returns special information from the database, particularly from the system table s.

A stored procedure residing in sybsystemprocs, which is provided by Sybase. System procedures provide shortcuts for retrieving information from the system table s, or mechanisms for accomplishing database administration and other tasks that involve updating system tables.

Tables in the master database that the system procedure s use to convert internal system values (for example, status bits) into human-readable format.

A user who controls security-related operations in Adaptive Server, including auditing, locking and unlocking login accounts, creating user-defined roles, and password management. See also System Administrator .

One of the data dictionary tables. System tables keep track of information about the Adaptive Server as a whole and about each user database. The master database contains some system tables that are not in user databases.