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Manual de usuario HP, modelo HP NonStop G-Series

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Tamaño del archivo: 487.56 kb
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Idioma del manual:itenfr
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Resumen del manual


Concurrency
An application can choose from two different concurrency types for a result set: read-only and updatable. A read-only result
set does not allow updates of its contents. An updatable result set allows rows to be updated, deleted, and inserted.
As with scrollable result sets, the JDBC Driver for SQL/MP might sometimes need to choose an alternative concurrency type
for a result set when the result set is created. Generally, queries that meet the following criteria produce an updatable result set:
The query references only a single table in the data base.
q
The query does not contain any join operations
q
The query selects the primary key of the table it references
q
The query selects all of the nonnullable columns in the underlying table
q
The query selects all columns that do not have a default value.
q
Batch Update Support
The batch update facility allows a Statement object to submit a set of update commands together as a single unit, or batch, to
the underlying database management system. The JDBC 2.0 documentation states that batch updates result in a performance
improvement. Because SQL/MP does not support batch updates, it is unlikely that a performance improvement can occur if
your application uses the batch update feature. Nevertheless, the batch update capability is available.
BLOBs and CLOBs
A BLOB represents a Binary Large OBject. A CLOB represents a Character Large OBject. BLOBs are typically used to store
images (such as GIFs) or serialized objects in the database. CLOBs are typically used to store large character data (such as an
XML file) in the database.
Because SQL/MP does not support either the Clob or the Blob data type, JDBC provides an alternative method that stores
the contents of a BLOB or CLOB in an Enscribe file and stores the name of that file in the column associated with the BLOB
or CLOB. From the point of view of the JDBC user, a BLOB or CLOB is any Java object that extends from the
java.lang.Object class. BLOBs and CLOBs must be serializable objects and must implement the
java.io.Serializable interface. This enables the JDBC driver to:
Serialize a
q
BLOB or CLOB object into an array of bytes to be stored in a BLOB/CLOB file.
Deserialize the contents of the BLOB/CLOB file to re-create the original object.
q
Because the JDBC driver creates and reads BLOBs and CLOBs in the same manner, the rest of this description refesr only to
BLOBs. You define a CLOB in exactly the same manner as a BLOB and use the BLOB syntax.
SQL/MP Table Definition
To use the Blob data type, you must define a column in the associated SQL/MP table to store the name of the Enscribe file
associated with that BLOB. The data type of the column should be either CHARACTER or VARCHAR and must be long enough
to store the Enscribe file name (at least 36 characters).
Creating a BLOB
A client JDBC application that needs to store a BLOB in an SQL/MP database table or retrieve a BLOB from an SQL/MP
database table provides a java.util.Properties object to the JDBC driver during connection time. This Properties
object provides the driver with all the information it needs to create or read the BLOB. An additional required property, called
a BlobMapFile property, specifies a unique file name in the $volume.subvolume.filename format. This file stores a
list of all the BLOB files created by a particular application. This file is later used by the Cleanup Utility to remove obsolete
BLOB files.
BlobInfoProperties
BlobInfo properties provide information about all table columns that are used to store BLOBs. Each BlobInfo property
consists of a key and value pair. The key is used to identify a unique BlobInfo property. The value specifies a particular
BLOB column in a table, the catalog for that table, and file locations where BLOB files should be created.

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Otros modelos de este manual:
Computadoras - HP NonStop L-Series (487.56 kb)

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