Glosario de Bases de Datos Sybase, "C"

See buffer cache .

For many processes, Adaptive Server uses an in-memory cache. The cache hit ratio is the percentage of times a needed page or result was found in the cache. For data pages, the cache hit ratio is the percentage of page requests that are serviced by the data cache compared to requests that require disk I/O.

A primary key or unique constraint column. A table can have multiple candidate keys.

All the possible combinations of the rows from each of the tables specified in a join. The number of rows in the Cartesian product is equal to the number of rows in the first table times the number of rows in the second table. Once the Cartesian product is formed, the rows that do not satisfy the join conditions are eliminated.

A delete operation that affects related data in other tables.

A type of system procedure that returns data from the system table s in tabular format.

Determines whether or not Adaptive Server automatically starts a new transaction on the next data retrieval or data modification statement. When chained transaction mode is set on outside a transaction, the next data retrieval or data modification statement begins a new transaction. This mode is ANSI compliant. It ensures that every SQL data retrieval and data modification statement occurs inside a transaction. Chained transaction mode may be incompatible with existing Transact-SQL programs. Chained transaction mode is off by default. Applications that require ANSI SQL (such as the Embedded SQL precompiler) should automatically set the chained option on at the beginning of each session.

An expression that returns a single character-type value. It can include literals, concatenation operators, functions, and column identifiers.

A set of specific (usually standardized) characters with an encoding scheme that uniquely defines each character. ASCII and ISO 8859-1 (Latin 1) are two common character sets.

Changing the encoding scheme of a set of characters on the way into or out of Adaptive Server. Conversion is used when Adaptive Server and a client communicating with it use different character sets. For example, if Adaptive Server uses ISO 8859-1 and a client uses Code Page 850, character set conversion must be turned on so that both server and client interpret the data passing back and forth in the same way.

A constraint placed on the check command that limits the values users can insert into a column of a table. A check constraint specifies the search_condition that values must pass before being inserted into the table.

The point at which all data pages that have been changed are guaranteed to have been written to the database device.

See Component Integration Services (CIS) .

A hierarchical level of security; for example, Top Secret, which has a higher classification value than Secret.

A set of keywords and options that tailor a Transact-SQL command to meet a particular need. Also called a keyword phrase.

The user's side of a client/server arrangement; can refer to the software making the calls to the server or to the machine running the client software.

A cursor declared through Open Client calls or Embedded SQL. Open Client keeps track of the rows returned from Adaptive Server and buffers them for the application. Updates and deletes to the result set of client cursors can be done only through Open Client calls.

A computer system architecture in which clients request a service and a server provides that service. Each machine can then specialize in the tasks it is best suited for.

A thread spawned to service a client request.

An index in which the physical order and the logical (indexed) order is the same. The leaf level of a clustered index represents the data pages themselves. A table can have only one clustered index.

See sort order .

A data value that describes one characteristic of an entity . A column contains an individual data item within a row or record. Also called a field.

Limit the values of a specified column. Place column-level constraints after the column name and datatype in the create table statement, before the delimiting comma.

An instruction that specifies an operation to be performed by the computer. Each command or SQL statement begins with a keyword, such as insert, that names the basic operation performed. Many SQL commands have one or more keyword phrase s, or clause s, that tailor the command to meet a particular need.

A permissions that applies to commands. See also object permission .

The end-of-batch signal that sends the batch to Adaptive Server for processing.

Symbols used to compare one value to another in a query. Comparison operators include equal to (=) greater than (>), less than (<), greater than or equal to (>=), less than or equal to (<=), not equal to (!=), not greater than (!>), and not less than (!<). See also arithmetic operators .

One of a set of non-hierarchical values used with classifications to make up a sensitivity label. Compartments usually represent topics or work groups.

Datatypes that are automatically converted for implicit or explicit comparison.

Any object that requires entries in the sysprocedures table, including check constraints, defaults, rules, stored procedures, triggers, and views. These objects are described by source text . Adaptive Server uses compiled objects to contain vital information about each database and to help you access and manipulate data.

Component Integration Services is a feature that extends Adaptive Server capabilities and provides enhanced interoperability. It is the core interoperability feature of OmniConnect. Component Integration Services allows Adaptive Server and OmniConnect to present a uniform view of enterprise data to client applications and provides location transparency to enterprise-wide data sources.

Indexes that involve more than one column. Use composite indexes when two or more columns are best searched as a unit because of their logical relationship.

An index key that includes two or more columns; for example, authors(au_lname, au_fname).

Combining expressions to form longer expressions. The expressions can include any combination of binary or character strings or column names.

Concurrent execution (multiprocessing) of independent and possibly competing processes or transactions.

In parallel sorts, consumer processes simultaneously sort a discrete range data received from producer processes. Consumer processe hand the sorted data off to a coordinating process

An expression that returns the same value each time the expression is used. In Transact-SQL syntax statements, a constant expression does not include variables or column identifiers.

A rule applied to a database object that ensures that all entries in the database object to which it applies satisfy a particular condition. For example, a column may have a constraint requiring that all values in the column be unique.

Protection that provides certain permissions or privileges depending on the identity of the user. This type of protection can be provided using views and the user_id built-in function.

A reserved database page that stores information about the last page of a partition .

A report or data display that breaks data into groups and generates summary information for each break. The breaks control the generation of summary data.

Transact-SQL's programming-like constructs (such as if, else , while, and goto) that control the flow of execution of Transact-SQL statements.

See character set conversion .

In parallel sorts, the coordinating process merges the results of the consumer processes into a single result set. For queries, the result set is the final, sorted data. For a create index statement, the coordinating process merges the sub-indexes into one, final index.

A subquery that cannot be evaluated independently, but depends on the outer query for its results. Also called a repeating subquery because the subquery is executed once for each row that might be selected by the outer query. See also nested queries .

Distinguish the different roles a particular table plays in a query, especially a correlated query or self-join . Assign correlation names in the from clause and specify the correlation name after the table name:

select au1.au_fname, au2.au_fname 
from authors au1, authors au2 
where au1.zip = au2.zip  

A measurable performance item that can be reported by the Windows NT Performance Monitor. This is generic Windows NT terminology for describing a mechanism for producing statistical performance information. Adaptive Server maintains a special set of counters to measure and report on Adaptive Server objects or events on the Windows NT platform.

See index covering .

See index covering .

A named select statement that retrieves one or more rows from a given table, and allows you to modify or delete the rows individually. Cursors consist of two parts: the cursor result set and the cursor position .

Indicates the current row of the cursor. You can explicitly reference that row using statements designed to support cursors, such as delete and. Change the current cursor position through fetch , which moves the current cursor position one or more rows down the cursor result set .

The set of rows resulting from the execution of the select statement associated with the cursor.

The process of generating a cursor result set .

The context in which the cursor is used. A cursor's existence depends on its scope: within a particular user session, within a stored procedure, or within a trigger.

A locking level or isolation level in which Adaptive Server has a shared lock on the base table pages that contain a current cursor row. The page remains locked until the cursor is no longer positioned on the page (as a result of fetches). If the base table has an index, the corresponding index pages have shared locks as well.