The Transact-SQL programming language provides several SET statements that change the current session handling of specific information. The SET statements are grouped into the categories shown in the following table.
- All SET statements are implemented at execute or run time, except for SET FIPS_FLAGGER, SET OFFSETS, SET PARSEONLY, and SET QUOTED_IDENTIFIER. These statements are implemented at parse time.
If a SET statement is run in a stored procedure or trigger, the value of the SET option is restored after control is returned from the stored procedure or trigger. Also, if a SET statement is specified in a dynamic SQL string that is run by using either sp_executesql or EXECUTE, the value of the SET option is restored after control is returned from the batch specified in the dynamic SQL string.
Stored procedures execute with the SET settings specified at execute time except for SET ANSI_NULLS and SET QUOTED_IDENTIFIER. Stored procedures specifying SET ANSI_NULLS or SET QUOTED_IDENTIFIER use the setting specified at stored procedure creation time. If used inside a stored procedure, any SET setting is ignored.
The user options setting of sp_configure allows for server-wide settings and works across multiple databases. This setting also behaves like an explicit SET statement, except that it occurs at login time.
Database settings set by using ALTER DATABASE are valid only at the database level and take effect only if explicitly set. Database settings override instance option settings that are set by using sp_configure.
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For any one of the SET statements with ON and OFF settings, you can specify either an ON or OFF setting for multiple SET options.
Note
This does not apply to the statistics related SET options.
For example, SET QUOTED_IDENTIFIER, ANSI_NULLS ON sets both QUOTED_IDENTIFIER and ANSI_NULLS to ON.
SET statement settings override equivalent database option settings that are set by using ALTER DATABASE. For example, the value specified in a SET ANSI_NULLS statement will override the database setting for ANSI_NULLs. Additionally, some connection settings are automatically set ON when a user connects to a database based on the values put into effect by the previous use of the sp_configure user options setting, or the values that apply to all ODBC and OLE/DB connections.
ALTER, CREATE and DROP DATABASE statements do not honor the SET LOCK_TIMEOUT setting.
When a global or shortcut SET statement, such as SET ANSI_DEFAULTS, sets several settings, issuing the shortcut SET statement resets the previous settings for all those options affected by the shortcut SET statement. If an individual SET option that is affected by a shortcut SET statement is explicitly set after the shortcut SET statement is issued, the individual SET statement overrides the corresponding shortcut settings.
When batches are used, the database context is determined by the batch established by using the USE statement. Ad hoc queries and all other statements that are executed outside the stored procedure and that are in batches inherit the option settings of the database and connection established by the USE statement.
Multiple Active Result Set (MARS) requests share a global state that contains the most recent session SET option settings. When each request executes it can modify the SET options. The changes are specific to the request context in which they are set, and do not affect other concurrent MARS requests. However, after the request execution is completed, the new SET options are copied to the global session state. New requests that execute under the same session after this change will use these new SET option settings.
When a stored procedure is executed, either from a batch or from another stored procedure, it is executed under the option values that are currently set in the database that contains the stored procedure. For example, when stored procedure db1.dbo.sp1 calls stored procedure db2.dbo.sp2, stored procedure sp1 is executed under the current compatibility level setting of database db1, and stored procedure sp2 is executed under the current compatibility level setting of database db2.
When a Transact-SQL statement refers to objects that reside in multiple databases, the current database context and the current connection context applies to that statement. In this case, if Transact-SQL statement is in a batch, the current connection context is the database defined by the USE statement; if the Transact-SQL statement is in a stored procedure, the connection context is the database that contains the stored procedure.
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When you are creating and manipulating indexes on computed columns or indexed views, the SET options ARITHABORT, CONCAT_NULL_YIELDS_NULL, QUOTED_IDENTIFIER, ANSI_NULLS, ANSI_PADDING, and ANSI_WARNINGS must be set to ON. The option NUMERIC_ROUNDABORT must be set to OFF.
If any one of these options is not set to the required values, INSERT, UPDATE, DELETE, DBCC CHECKDB and DBCC CHECKTABLE actions on indexed views or tables with indexes on computed columns will fail. SQL Server will raise an error listing all the options that are incorrectly set. Also, SQL Server will process SELECT statements on these tables or indexed views as if the indexes on computed columns or on the views do not exist.
参考链接
- http://technet.microsoft.com/en-us/library/ms190356.aspx#feedback
- http://sqlserverrider.wordpress.com/2013/05/12/control-current-session-and-specific-information-sql-server-set-statements/