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SQL Building Blocks and Server Settings

Aug 6, 2004

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This chapter is from the book 

Transact-SQL Desk Reference: For Microsoft SQL Server

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2.7 SYSTEM STORED PROCEDURES AND DBCC

System stored procedures and extended procedures are built-in commands that perform a variety of tasks to do database administration and to provide information.

2.7.1 System Stored Procedures

There are hundreds of system stored procedures and extended procedures. Some individual stored procedures will be described as needed throughout the book. You may check the index to see if a given stored procedure is described in the book. A complete list of system stored procedures may be found in Appendix A. Metadata stored procedures are discussed on p. 376. Additional details may be found by looking each up by name in Books Online.

In general, system stored procedure names start with sp_ and return results within SQL Server. Extended stored procedure names start with xp_ and require doing work outside of SQL Server such as making calls to the operating system or an external process.

Some useful system stored procedures and extended procedures are summarized in Table 2-71.

Table 2-71. System Stored Procedures

sp_configure [settingname [, settingvalue]]	No arguments—lists all current server settings in five columns name minimum maximum config_value run_value where config_value is value configured but may not yet be effective until server restarts or "reconfigure" command is executed. 1 argument—shows its value; 2 arguments—sets its value See page 177 for discussion and examples.
sp_dboption	Included for backward compatibility. Use ALTER DATABASE.
sp_help [objname]	No arguments—lists all objects in the current database. 1 argument—reports information about the database object in the current database.
sp_helpdb dbname	Reports information about a specified database or all databases.
sp_helpindex tablename	Reports indexes on the table or view.
sp_helptext objname	Prints the code text of a rule, a default or an unencrypted stored procedure, user-defined function, trigger or view.
sp_lock [spid]	Reports locks held by all processes or by spid (page 140).
sp_who	Reports all current users and processes connected to SQL Server.
xp_cmdshell	Executes a given command string as an operating system command shell and returns any output as rows of text.
xp_grantlogin	Grants a Microsoft Windows NT group or user access to Microsoft SQL Server.
xp_revokelogin	Revokes access from a Microsoft Windows NT group or user to Microsoft SQL Server.

Stored procedures are executed using the following syntax.

Syntax

[EXEC[UTE]]   sp_stored_procedure_name

EXEC or EXECUTE keyword is optional if this is the first statement in a batch.

2.7.1.1 The sp_ Procedures

The stored procedures provided by SQL server that begin with sp_ are predefined to provide administrative functions for managing SQL Server and displaying information about databases and users. Examples include the following: sp_helpdb, sp_help, sp_configure. See a complete list in Appendix A.

Example: Use sp_helpdb to display size and file information about pubs database.

SQL
EXEC sp_helpdb pubs

Result
name db_size owner dbid created ... ------- ---------- -------- ------ ---------- ... pubs 2.00 MB sa 5 Aug 6 2000 ... name fileid filename ... ------- ------ ----------- ... pubs 1 C:\Program Files\Microsoft SQL Server\MSSQL\data\pubs.mdf ... pubs_log 2 C:\Program Files\Microsoft SQL Server\MSSQL\data\pubs_log.ldf ...

2.7.1.2 The xp_ Procedures—Provided

The procedures that begin with xp_, called extended stored procedures, allow creation of external routines in a programming language such as C. They are used to do work outside of SQL Server, such as accessing the registry, etc. A competent user may create his or her own extended stored procedures with sp_addextendedproc. Some examples include the following: xp_cmdshell, xp_grantlogin, xp_revokelogin. For more details, see Books Online Index: xp_.

Example: Use xp_cmdshell to show contents of C:\directory on server machine.

SQL
EXEC master..xp_cmdshell 'dir/w C:\'

Result
output ---------------------------------------------------------------------- Volume in drive C is AMY_C Volume Serial Number is 2CA0-6A55 Directory of C:\ boot.ini [Documents and Settings] [HySnap] [Inetpub] [WINNT] File(s) 189 bytes 4 Dir(s) 9,494,585,344 bytes free

Example: Display the names of database objects in the pubs database.

SQL
USE pubs go EXEC sp_help -- List all database objects in pubs database

Result
Name Owner Object_type ------------------------------ ------------ --------------- titlevie dbo view authors dbo user table discounts dbo user table employee dbo user table ... titleauthor dbo user table titles dbo user table syscolumns dbo system table syscomments dbo system table ... PK__jobs__117F9D94 dbo primary key cns PK_emp_id dbo primary key cns UPK_storeid dbo primary key cns UPKCL_auidind dbo primary key cns ... FK__discounts__stor___0F975522 dbo foreign key cns ... DF__authors__phone__78B3EFCA dbo default (maybe cns) ... CK__authors__au_id__77BFCB91 dbo check cns ... User_type Storage_type Length Prec Scale Nullable Default_name Collation ------------ --------------- --------- ----- ---- ----- ------- ------------------------------------- empid char 9 9 NULL no none SQL_Latin1_General_CP1_CI_AS id varchar 11 11 NULL no none SQL_Latin1_General_CP1_CI_AS tid varchar 6 6 NULL no none SQL_Latin1_General_CP1_CI_AS

Example: Display the metadata for the authors table of the pubs database including column names.

SQL
EXEC sp_help authors -- Show structure and properties of "authors" table in pubs database

Result
Name Owner Type Created_datetime ------------ ------- ---------- ----------------------- authors dbo user table 2000-08-06 01:33:52.123 Column_name Type Computed Length Prec Scale Nullable ------------ ------- ------------- --------- ------ ------- ----------- au_id id no 11 no au_lname varchar no 40 no au_fname varchar no 20 no ...

2.7.2 DBCC

The initials DBCC stand for Database Console Command (a k a Database Consistency Checker before SQL Server 2K). DBCC statements check the physical and logical consistency of a database. Many DBCC statements can fix detected problems.

The four categories of DBCC statements and descriptions are shown in Tables 2-72 through 2-75 below. See Books Online for details.

2.7.2.1 DBCC Maintenance Statements

The commands listed in Table 2-72 will help you perform maintenance tasks on a database, index or filegroup.

Table 2-72. DBCC Maintenance Statements

DBCC DBREINDEX	Rebuilds one or more indexes for a table in the specified database.
DBCC DBREPAIR	Drops a damaged database. NOTE: DBCC DBREPAIR is included in Microsoft SQL Server 2000 for backward compatibility only and may not appear in future versions. DROP DATABASE is recommended to drop damaged databases.
DBCC INDEXDEFRAG	Defragments indexes of the specified table or view.
DBCC SHRINKDATABASE	Shrinks the size of the data files in the specified database.
DBCC SHRINKFILE	Shrinks the size of the specified data file or log file for the related database.
DBCC UPDATEUSAGE	Reports and corrects inaccuracies in the sysindexes table. This may result in incorrect space usage reports by sp_spaceused.

2.7.2.2 DBCC Miscellaneous Statements

The commands in Table 2-73 will help you do miscellaneous tasks such as enabling row-level locking or removing a DLL from memory.

Table 2-73. DBCC Miscellaneous Statements

DBCC dllname (FREE)	Unloads the specified extended stored procedure dynamic-link library (DLL) from memory.
DBCC HELP	Returns syntax information for the specified DBCC statement.
DBCC PINTABLE	Marks a table to be pinned, which means Microsoft SQL Server does not flush the pages for the table from memory.
DBCC ROWLOCK	Does not affect the locking behavior of SQL Server 2K. It is included for backward compatibility for SS 6.5 scripts and may not appear in future versions.
DBCC TRACEOFF	Disables the specified trace flag(s).
DBCC TRACEON	Turns on (enables) the specified trace flag.
DBCC UNPINTABLE	Marks a table as unpinned. After a table is marked as unpinned, the table pages in the buffer cache can be flushed.

2.7.2.3 DBCC Status Statements

The commands listed in Table 2-74 allow you to perform status checks.

Table 2-74. DBCC Status Statements

DBCC INPUTBUFFER	Displays the last statement sent from a client to Microsoft SQL Server.
DBCC OPENTRAN	Displays information about the oldest active transaction and the oldest distributed and nondistributed replicated transactions, if any, within the specified database. Results are displayed only if there is an active transaction or if the database contains replication information. An informational message is displayed if there are no active transactions.
DBCC OUTPUTBUFFER	Returns the current output buffer in hexadecimal and ASCII format for the specified system process ID (SPID).
DBCC PROCCACHE	Displays information in a table format about the procedure cache.
DBCC SHOWCONTIG	Displays fragmentation information for the data and indexes of the specified table.
DBCC SHOW_STATISTICS	Displays the current distribution statistics for the specified target on the specified table.
DBCC SQLPERF	Provides statistics about the use of transaction-log space in all databases.
DBCC TRACESTATUS	Displays the status of trace flags.
DBCC USEROPTIONS	Returns the SET options active (set) for the current connection.

2.7.2.4 DBCC Validation Statements

The commands shown in Table 2-75 allow you to perform validation operations on a database, table, index, catalog, filegroup, system tables or allocation of database pages.

Table 2-75. DBCC Validation Statements

DBCC CHECKALLOC	Checks consistency of disk space allocation structures of specified database.
DBCC CHECKCATALOG	Checks for consistency in and between system tables in specified database.
DBCC CHECKCONSTRAINTS	Checks integrity of a specified constraint or all constraints on the specified table.
DBCC CHECKDB	Checks the allocation and structural integrity of all the objects in the specified database.
DBCC CHECKFILEGROUP	Checks the allocation and structural integrity of all tables in the current database in the specified filegroup.
DBCC CHECKIDENT	Checks the current identity value for the specified table and, if needed, corrects the identity value.
DBCC CHECKTABLE	Checks the integrity of the data, index, text, ntext and image pages for the specified table or indexed view.
DBCC NEWALLOC	DBCC NEWALLOC is identical to DBCC CHECKALLOC which is recommended. DBCC NEWALLOC is included in SS 2000 for backward compatibility and may not appear in future versions.

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