SQL/MX Glossary

Glossary

HP NonStop SQL/MX Glossary—523732-002

Glossary-29

read committed access

read committed access. An access option for any DML statement that requires that the

data being accessed is from committed rows. SQL/MX requires that a lock can be

acquired on the data requested by the DML statement, but does not actually lock the

data, thereby reducing lock request conflicts. If a lock cannot be granted (implying that

the row contains uncommitted data), the DML statement request waits until the lock in

place is released. Contrast with read uncommitted access and serializable access.

read uncommitted access. An access option for the SELECT statement that gives users

immediate access to data when a transaction in progress might be changing the data.

The data accessed need not be from committed rows. With read uncommitted access,

a process does not acquire a lock on the data it accesses and does not test for existing

locks before reading data. Contrast with read committed access and serializable

access.

recompilation. See automatic SQL recompilation or explicit SQL compilation.

record. A unit of data that can be read from or written to a file; a record is represented as a

row in a relational table.

record locks. A lock held by a process on one specific record; corresponds to row lock.

recovery. The returning of a database file or files to a consistent state.

referential integrity. A SQL-92 feature that prevents users or applications from entering

inconsistent data. The SQL/MX ALTER TABLE statement allows you to set referential

constraints for tables to declare that a column or set of columns (called a foreign key)

can contain only values that match those in a column or set of columns specified in the

REFERENCES clause. The two columns or sets of columns must have the same

characteristics (data type, length, scale, precision). There must also be a UNIQUE or

PRIMARY KEY constraint on the column or set of columns specified in the

REFERENCES clause. The foreign key is the column or set of columns specified in the

FOREIGN KEY clause, immediately following the FOREIGN KEY keywords.

the local node.

regular identifier. Names beginning with a letter (A through Z or a through z), that can also

contain other letters, digits (0-9), or the underbar character (_). Regular Identifiers are

not case-sensitive. See also delimited identifier.

related catalogs. The relationship between catalogs when objects from one catalog depend

upon objects from another catalog because of a trigger, view, or constraint. Related

catalogs must have identical visibility; that is, be registered on the same set of nodes.

relational database. A database in which data is represented as tables.

Remote Duplicate Database Facility (RDF). An HP NonStop data replication product that

monitors changes made to a production database on a local (primary) system and

maintains a copy of that database on one or more remote (backup) systems.