Hướng dẫn học Microsoft SQL Server 2008 part 97 pdf

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Part VI Enterprise Data Management
TABLE 39-8
Cursor-Configuration Properties
Property Level* Graphic Control Code Option
Cursor Threshold S Management Studio EXEC sp_configure ‘cursor
threshold’
Cursor Close on
Commit
SDC Management Studio ALTER DATABASE <DB Name> SET
cursor_close_on_commit
Cursor Default D Management Studio ALTER DATABASE <DB Name> SET
cursor_default
* The configuration level refers to Server, Database, or Connection.
For information about cursor concepts, writing, and avoiding cursors, refer to Chapter 22,
‘‘Kill the Cursor!’’
Cursor threshold
The cursor threshold property sets the number of rows in a cursor set before the cursor keysets
are generated asynchronously. The Query Optimizer estimates the number of rows that will be returned
from the result set. If the estimated number of rows is greater than the
cursor threshold, then the
cursor is generated asynchronously; otherwise, it is generated synchronously, causing a delay because the
query has to wait until all the rows are fetched. Every cursor keyset will be generated asynchronously if
the
cursor threshold property is set to 0.
The default of
-1 causes all keysets to be generated synchronously, which is OK for smaller keysets. For
larger cursor keysets, though, this may be a problem.
In Management Studio, the
cursor threshold option can be set to the desired value in the ‘‘Cursor
threshold’’ box in the Server Properties Advanced tab (refer to Figure 39-9).

When you are working with cursors, the following code will permit synchronous cursor keysets for cur-
sors of up to 10,000 rows:
EXEC sp_configure ‘show advanced options’, 1;
RECONFIGURE;
EXEC sp_configure ‘cursor threshold’, 10000;
RECONFIGURE;
Cursor close on commit
This property will close an open cursor after a transaction is committed when set to ON.Ifitissetto
OFF (the default), then cursors remain open across transactions until a close cursor statement is
issued.
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The CURSOR_CLOSE_ON_COMMIT option can be set from Management Studio and code at the server,
database, and connection level. In Management Studio, the
CURSOR_CLOSE_ON_COMMIT option can be
turned on at the various levels as follows:
■ Server level: Check the ‘‘cursor close on commit’’ checkbox in the Server properties Connec-
tions tab (refer to Figure 39-8).
■ Database level: Select
True for the ‘‘cursor close on commit enabled’’ box in the Database
Properties Options tab (refer to Figure 39-2).
■ Connection level: To set this property for current queries, click the Query menu ➪ Query
Options ➪ Execution ➪ ANSI and check the
SET CURSOR_CLOSE_ON_COMMIT check box.
To set this property for all future connections, click the Tools menu ➪ Options ➪ Query
Execution ➪ ANSI and check the
SET CURSOR_CLOSE_ON_COMMIT check box.
To set

CURSOR_CLOSE_ON_COMMIT in code, do the following:
■ Server level
EXEC sp_configure ‘user options’, 4;
RECONFIGURE;
■ Database level (example to set the option on for the AdventureWorks2008 sample database)
ALTER DATABASE AdventureWorks2008 SET CURSOR_CLOSE_ON_COMMIT ON;
■ Connection level
SET CURSOR_CLOSE_ON_COMMIT ON;
Cursor default
This property will make each cursor local to the object that declared it when set to local.Whenitis
set to
global (the default), the cursor’s scope can be extended outside the object that created it.
In Management Studio, the
CURSOR_DEFAULT option can be set to the desired scope in the ‘‘Default
cursor’’ box in the Database Properties Options tab (refer to Figure 39-2).To set the cursor default for
the
AdventureWorks2008 sample database to LOCAL in code, do the following:
ALTER DATABASE AdventureWorks2008 SET CURSOR_DEFAULT LOCAL;
SQL ANSI–configuration properties
The SQL ANSI–configuration properties, shown in Table 39-9, are used to set ANSI behavior in SQL
Server.
The connection default properties (there are several) affect the environment of batches executed within a
connection. Most of the connection properties change SQL Server behavior so that it complies with the
ANSI standard. Because so few SQL Server installations modify these properties, it’s much safer to mod-
ify them in code at the beginning of a batch than to set them at the server or database level.
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Part VI Enterprise Data Management
TABLE 39-9

SQL ANSI–Configuration Properties
Property Level* Graphic Control Code Option
ANSI Defaults C Management Studio SET ANSI_DEFAULTS
ANSI Null Behavior SDC Management Studio ALTER DATABASE <DB Name> SET
ANSI_NULL_DFLT_OFF
SET ANSI_NULL_DFLT_ON
ANSI Nulls SDC Management Studio ALTER DATABASE <DB Name> SET
ANSI_NULLS
ANSI Padding SDC Management Studio ALTER DATABASE <DB Name> SET
ANSI_PADDING
ANSI Warnings SDC Management Studio ALTER DATABASE <DB Name> SET
ANSI_WARNINGS
Arithmetic Abort SDC Management Studio ALTER DATABASE <DB Name> SET
arithabort
Arithmetic Ignore SC - SET ARITHIGNORE
Numeric Round Abort SDC Management Studio ALTER DATABASE <DB Name> SET
NUMERIC_ROUNDABORT{ON | OFF}
Null Concatenation SDC Management Studio ALTER DATABASE <DB Name> SET
CONCAT_NULL_YIELDS_NULL
Use Quoted Identifier SD Management Studio ALTER DATABASE <DB Name> SET
QUOTED_IDENTIFIER
* The configuration level refers to Server, Database, or Connection.
For example, T-SQL requires a begin transaction to start a logical unit of work. Oracle assumes
a
begin transaction is at the beginning of every batch. If you prefer to work with implicit (non-
stated) transactions, then you’re safer setting the implicit transaction connection property at the begin-
ning of your batch. For these reasons, I recommend leaving the connection properties at the default val-
ues and setting them in code if needed.
The SQL ANSI-configuration settings are set at three levels: server, database and connection, as indicated
in Table 39-9. The

sp_configure system stored procedure has the ‘‘user options’’ setting that allows
manipulation of server-wide ANSI settings and it works across databases. The
ALTER DATABASE com-
mand can be used to set the default database setting for ANSI. Connection-level settings are performed
with the
SET command and they override the default database setting.
In Management Studio, the ANSI settings can be enabled (
ON) at the three levels as follows:
■ Server level: In the Server properties Connections tab (refer to Figure 39-8), check the boxes
for the ANSI settings that you want to enable.
■ Database level: In the Database Properties Options tab (refer to Figure 39-2 above), enable
the ANSI settings.
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Configuring SQL Server 39
■ Connection level: Click the Query menu ➪ Query Options ➪ Execution ➪ ANSI, and then
check the boxes for the ANSI settings that you want to enable.
For backward compatibility, the sp_dboption stored procedure is also available, but using
this procedure is not recommended because it will be removed in future versions of SQL
Server.
You can change the default ANSI database settings in model system database and then the defaults will
be changed for all future databases.
The database setting for ANSI overwrites the server setting, and the connection setting overwrites the
server and database setting.
ANSI defaults
SQL Server provides the SET ANSI_DEFAULTS command to manage a group of SQL Server settings.
When
SET ANSI_DEFAULTS is enabled, it provides the following settings (explained later in this
section):

■
SET ANSI_NULLS
■ SET ANSI_NULL_DFLT_ON
■ SET ANSI_PADDING
■ SET ANSI_WARNINGS
■ SET CURSOR_CLOSE_ON_COMMIT
■ SET IMPLICIT_TRANSACTIONS
■ SET QUOTED_IDENTIFIER
To set ANSI_DEFAULTS in code, do the following:
SET ANSI_DEFAULTS ON;
ANSI null default
The ANSI_NULL_DEFAULT setting controls the default nullability. This setting is used when a
NULL or NOT_NULL is not explicitly specified when creating a table. The default database setting for
ANSI_NULL_DEFAULT is OFF.
To set the
ANSI_NULL_DEFAULT option to ON for the AdventureWorks2008 sample database in
code, do the following:
ALTER DATABASE AdventureWorks2008 SET ANSI_NULL_DEFAULT ON;
If the ANSI_NULL_DEFAULT option is not set at the database level, you can set the nullability of new
columns using the
SET ANSI_NULL_DFLT_ON and SET ANSI_NULL_DFLT_OFF commands. SET
ANSI_NULL_DFLT_ON
can be enabled to allow null values at the connection level:
SET ANSI_NULL_DFLT_ON ON;
SET ANSI_NULL_DFLT_OFF
can be enabled to not allow null values at the connection level:
SET ANSI_NULL_DFLT_OFF ON;
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Part VI Enterprise Data Management
To enable ANSI_NULL_DFLT_ON at the server level in code, do the following:
EXEC sp_configure ‘user options’, 1024;
RECONFIGURE;
The following enables ANSI_NULL_DFLT_OFF at the server level:
EXEC sp_configure ‘user options’, 2048;
RECONFIGURE;
You cannot set both the SET ANSI_NULL_DFLT_ON and the SET ANSI_NULL_DFLT_OFF com-
mands to
ON at the same time. Either one can be ON and the other can be OFF or both can
be
OFF.
ANSI NULLs
The ANSI_NULLS connection setting is used to determine comparison evaluations. When set to ON,all
comparisons to a null value will evaluate to
UNKNOWN.WhensettoOFF, the comparison to a null value
will evaluate to
true if both values are NULL. The default database setting for ANSI_NULLS is OFF.
The following enables
ANSI_NULLS at the connection level:
SET ANSI_NULLS ON;
If SET ANSI_NULLS is not specified, then the settings of ANSI_NULLS of the current database apply.
To enable
ANSI_NULLS for the AdventureWorks2008 sample database in code, do the following:
ALTER DATABASE AdventureWorks2008 SET ANSI_NULLS ON;
The following enables ANSI_NULLS at the server level:
EXEC sp_configure ‘user options’, 32;
RECONFIGURE;
The ANSI_NULLS option is deprecated and will always be ON in a future version of SQL
Server.

ANSI padding
The ANSI_PADDING connection setting affects o nly newly created columns. When set to ON,data
stored in
char, varchar, binary,andvarbinary data types will retain any padded zeros to the
left of variable binary numbers, and any padded spaces to the right or left of variable-length characters.
When set to
OFF, all leading and trailing blanks and zeros are trimmed. The default database setting for
ANSI_PADDING is OFF.
The following enables
ANSI_PADDING in code at the connection level:
SET ANSI_PADDING ON;
If SET ANSI_PADDING is not specified, then the settings of ANSI_PADDING of the current database
apply. The following enables
ANSI_PADDING for the AdventureWorks2008 sample database:
ALTER DATABASE AdventureWorks2008 SET ANSI_PADDING ON;
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Configuring SQL Server 39
This enables ANSI_PADDING at the server level in code:
EXEC sp_configure ‘user options’, 16;
RECONFIGURE;
The ANSI_PADDING option is deprecated and will always be ON in a future version of SQL
Server
.
ANSI warnings
The ANSI_WARNINGS connection setting is used to handle ANSI errors and warnings such as arithmetic
overflow, divide-by-zero and null values appearing in aggregate functions. The default database setting
for
ANSI_WARNINGS is OFF. When this setting is OFF, no warnings are raised when null values appear

in aggregate functions, and null values are returned when divide-by-zero occurs and overflow errors
occur. When the setting is
ON, the query is aborted and errors are raised when arithmetic overflow
errors and divide-by-zero occurs.
To set
ANSI_WARNINGS in code at the connection level:
SET ANSI_WARNINGS ON;
If SET ANSI_WARNINGS is not specified, then the settings of ANSI_WARNINGS of the current database
apply. The following enables
ANSI_WARNINGS for the AdventureWorks2008 sample database:
ALTER DATABASE AdventureWorks2008 SET ANSI_WARNINGS ON;
Use the following to enable ANSI_WARNINGS at the server level in code:
EXEC sp_configure ‘user options’, 8;
RECONFIGURE;
Arithmetic abort
The ARITHABORT connection setting is used to handle query termination if arithmetic errors such as
data overflow or divide-by-zero occurs. The default database setting for
ARITHABORT is OFF.
What exactly is terminated also depends on the
ANSI_WARNINGS setting. Table 39-10 explains the
behavior based on the values of
ANSI_WARNINGS and ARITHABORT.
To set
ARITHABORT in code at the connection level:
SET ARITHABORT ON;
If ARITHABORT is not specified, then the settings of the current database apply. To enable
ARITHABORT for AdventureWorks2008 sample database in code, do the following:
ALTER DATABASE AdventureWorks2008 SET ARITHABORT ON;
The following enables ARITHABORT at the server level:
EXEC sp_configure ‘user options’, 64;

RECONFIGURE;
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Part VI Enterprise Data Management
TABLE 39-10
ANSI_WARNINGS and ARITHABORT Behavior
ARITHABORT ANSI_WARNINGS Behavior
ON ON Query is aborted
ON OFF Batch is aborted or transaction is rolled back
OFF ON Query is aborted
OFF OFF No warning is raised and null is returned
Arithmetic ignore
The ARITHIGNORE connection setting is used to control whether an error message is returned from
arithmetic overflow or divide-by-zero errors. To abort the query, you need to use the
ARITHABORT
setting. Both ARITHABORT and ARITHIGNORE can be set to ON but ARITHABORT takes precedence
over
ARITHIGNORE.TosetARITHIGNORE in code, use the following:
SET ARITHIGNORE ON;
The following enables ARITHIGNORE at the server level:
EXEC sp_configure ‘user options’, 128;
RECONFIGURE;
Numeric round abort
The NUMERIC_ROUNDABORT connection setting is used to control the behavior of numeric decimal-
precision-rounding errors in process. When
NUMERIC_ROUNDABORT is set to ON and ARITHABORT
is set to ON, an error is generated and no result is returned if the numeric-decimal precision is lost in
an expression value. Loss of numeric-decimal precision can occur when a value with fixed precision is
stored in a c olumn or variable with less precision.

If
ARITHABORT is set to OFF and NUMERIC_ROUNDABORT is set to ON, a warning appears and null is
returned. When
NUMERIC_ROUNDABORT is set to OFF, the process will proceed without errors or warn-
ings, and the result is rounded down to the precision of the object in which the number is being stored.
The default database setting for
NUMERIC_ROUNDABORT is OFF.
To set
NUMERIC_ROUNDABORT in code at the connection level:
SET NUMERIC_ROUNDABORT ON;
If NUMERIC_ROUNDABORT is not specified, then the settings of the current database apply. The follow-
ing enables
NUMERIC_ROUNDABORT for the AdventureWorks2008 sample database:
ALTER DATABASE AdventureWorks2008 SET NUMERIC_ROUNDABORT ON;
To enable NUMERIC_ROUNDABORT at the server level in code, do the following:
EXEC sp_configure ‘user options’, 8192;
RECONFIGURE;
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Configuring SQL Server 39
Concatenation null yields null
The CONCAT_NULL_YIELDS_NULL setting is used to control the behavior of the r esult when con-
catenating a string with a
null.WhensettoON, any string concatenated with a null will result in a
null.WhensettoOFF, any string concatenated with a null will result in the original string, ignoring
the
null. The default database setting for CONCAT_NULL_YIELDS_NULL is OFF.
The following sets
CONCAT_NULL_YIELDS_NULL at the connection level:

SET CONCAT_NULL_YIELDS_NULL ON;
If CONCAT_NULL_YIELDS_NULL is not specified, then the settings of the current database apply. The
following enables
CONCAT_NULL_YIELDS_NULL for the AdventureWorks2008 sample database:
ALTER DATABASE AdventureWorks2008 SET CONCAT_NULL_YIELDS_NULL ON;
The following enables CONCAT_NULL_YIELDS_NULL at the server level:
EXEC sp_configure ‘user options’, 4096;
RECONFIGURE;
Use quoted identifier
The QUOTED_IDENTIFIER setting enables you to refer to an identifier, such as a column name, by
enclosing it within double quotes. When set to
ON, identifiers can be delimited by double quotation
marks. When set to
OFF, identifiers cannot be placed in quotation marks and must not be keywords.
The default database setting for
QUOTED_IDENTIFIER is OFF.
This sets
QUOTED_IDENTIFIER to ON at the connection l evel:
SET QUOTED_IDENTIFIER ON;
If QUOTED_IDENTIFIER is not specified, then the settings of the current database apply. To enable
QUOTED_IDENTIFIER for the AdventureWorks2008 sample database, use the following:
ALTER DATABASE AdventureWorks2008 SET QUOTED_IDENTIFIER ON;
This enables QUOTED_IDENTIFIER at the server level:
EXEC sp_configure ‘user options’, 256;
RECONFIGURE;
When dealing with indexes on computed columns and indexed views, four of these
defaults (
ANSI_NULLS, ANSI_PADDING, ANSI_WARNINGS,andQUOTED_IDENTIFIER)mustbe
set to
ON.

Trigger configuration properties
The trigger configuration properties, shown in Table 39-11, are used to control trigger behavior in SQL
Server.
Trigger behavior can be set at both the server and database levels.
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Part VI Enterprise Data Management
TABLE 39-11
Trigger Configuration Properties
Property Level* Graphic Control Code Option
Allow Nested Triggers S Management Studio EXEC sp_configure ‘nested
triggers’
Recursive Triggers D Management Studio ALTER DATABASE <DB Name> SET
recursive_triggers
* The configuration level refers to Server, Database, or Connection.
Nested triggers
A trigger is a small stored procedure that is executed on an insert, update,ordelete operation
on a table. Triggers are nested when a trigger performs an action that initiates another trigger, which
can initiate another trigger, and so on. Triggers can be nested up to 32 levels. The
nested triggers
server configuration option can be used to control whether AFTER triggers can be nested triggers.
In Management Studio, the
nested trigger option can be set by selecting True (default) or False in
the ‘‘Allow Triggers to Fire Others’’ option in the Server Properties Advanced tab (refer to Figure 39-9).
To turn
nested triggers OFF in code, do the following:
EXEC sp_configure ‘nested triggers’, 0;
RECONFIGURE;
INSTEAD OF triggers can be nested regardless of the setting of this option.

Recursive triggers
If the code in the trigger inserts, updates, or deletes the same table again, then the trigger causes itself to
be executed again. Recursion can also occur if the code in the trigger fires and performs an action that
causes a trigger on another table to fire. This second trigger performs an action that causes an update to
occur on the original table, which causes the original trigger to fire again. Recursive behavior is enabled
or disabled by the recursive trigger database option. By default, the
RECURSIVE_TRIGGERS option is
set to
OFF.
In Management Studio, the recursive triggers option can be enabled by selecting True in the ‘‘Recursive
Triggers Enabled’’ option in the Database Properties Options tab (refer to Figure 39-2).
The following sets the recursive triggers option
ON in the AdventureWorks2008 sample database in
T-SQL code:
ALTER DATABASE AdventureWorks2008 SET RECURSIVE_TRIGGERS ON;
The server property nested triggers and the database property recursive triggers are
often confused with each other. Refer to Chapter 26, ‘‘Creating DML Triggers,’’ for a com-
plete explanation, including coverage of how triggers can call other triggers and how these properties
control trigger behavior.
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Configuring SQL Server 39
Database-state-configuration properties
The database-state-configuration properties, shown in Table 39-12, are available in SQL Server. These
configurations are mostly used when a DBA is performing maintenance on the database.
The state of the database can be set with the
ALTER DATABASE command. The sp_dboption com-
mand is also available for backward compatibility. However, using the
sp_dboption command it is

not recommended because it will be removed in future versions of SQL Server.
Database-access level
The database-access-configuration options are used to set the state of the database. When the database is
offline, no access to the database is allowed.
To set
AdventureWorks2008 sample database to an OFFLINE state in code, do the following:
ALTER DATABASE AdventureWorks2008 SET OFFLINE;
TABLE 39-12
Database-State-Configuration Properties
Property Level* Graphic Control Code Option
Database OffLine D Management Studio ALTER DATABASE <DB Name> SET
OFFLINE
Database OnLine D Management Studio ALTER DATABASE <DB Name> SET
ONLINE
Emergency D - ALTER DATABASE <DB Name> SET
EMERGENCY
Read-Only D Management Studio ALTER DATABASE <DB Name> SET
READ_ONLY
Restricted
Access — Members of
db_owner, dbcreator,
or sysadmin
D Management Studio ALTER DATABASE <DB Name> SET
RESTRICTED_USER
Restricted
Access — Single user
D Management Studio ALTER DATABASE <DB Name> SET
SINGLE_USER
Multi User D Management Studio ALTER DATABASE <DB Name> SET
MULTI_USER

Compatibility Level D Management Studio ALTER DATABASE <DB NAME> SET
COMPATIBILITY_LEVEL
* The configuration level refers to Server, Database, or Connection.
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