System Base Tables
Applies to: 
SQL Server
Azure SQL Managed Instance
System base tables are the underlying tables that actually store the metadata for a specific database. The master database is special in this respect because it contains some additional tables that are not found in any of the other databases. These tables contain persisted metadata that has server-wide scope.
Important
The system base tables are used only within the SQL Server Database Engine and are not for general customer use. They are subject to change and compatibility is not guaranteed.
System Base-Table Metadata
A grantee that has CONTROL, ALTER, or VIEW DEFINITION permission on a database can see system base table metadata in the sys.objects catalog view. The grantee can also resolve the names and object IDs of system base tables by using built-in functions such as OBJECT_NAME and OBJECT_ID.
To bind to a system base table, a user must connect to the instance of SQL Server by using the dedicated administrator connection (DAC). Trying to execute a SELECT query from a system base table without connecting by using DAC raises an error.
Important
Access to system base tables by using DAC is designed only for Microsoft personnel, and it is not a supported customer scenario.
System Base Tables
The following table lists and describes each system base table in SQL Server.
| Base table | Description |
|---|---|
| sys.sysschobjs | Exists in every database. Each row represents an object in the database. |
| sys.sysbinobjs | Exists in every database. Contains a row for each Service Broker entity in the database. Service Broker entities include the following: Message type Service contract Service The names and types use binary collation that is fixed. |
| sys.sysclsobjs | Exists in every database. Contains a row for each classified entity that shares the same common properties that include the following: Assembly Backup device Full-text catalog Partition function Partition scheme File group Obfuscation key Schema |
| sys.sysnsobjs | Exists in every database. Contains a row for each namespace-scoped entity. This table is used for storing XML collection entities. |
| sys.syscolpars | Exists in every database. Contains a row for every column in a table, view, or table-valued function. It also contains rows for every parameter of a procedure or function. |
| sys.systypedsubobjs | Exists in every database. Contains a row for each typed subentity. Only parameters for partition function fall into this category. |
| sys.sysidxstats | Exists in every database. Contains a row for each index or statistics for tables and indexed views Note: Every index (except heap) is associated with a statistic that has the same name as the index. |
| sys.sysiscols | Exists in every database. Contains a row for each persisted index and statistics column. |
| sys.sysscalartypes | Exists in every database. Contains a row for each user-defined or system type. |
| sys.sysdbreg | Exists in the master database only. Contains a row for each registered database. |
| sys.sysxsrvs | Exists in the master database only. Contains a row for each local, linked, or remote server. |
| sys.sysrmtlgns | This system base table exists in the master database only. Contains a row for each remote login mapping. This is used to map incoming logins that claim to be coming from a corresponding server to an actual local login. |
| sys.syslnklgns | Exists in the master database only. Contains a row for each linked login mapping. Linked login mappings are used by remote procedure calls and distributed queries that emanate from a local server out to a corresponding linked server. |
| sys.sysxlgns | Exists in the master database only. Contains a row for each server principal. |
| sys.sysdbfiles | Exists in every database. If the column dbid is zero, the row represents a file that belongs to this database. In the master database, the column dbid can be nonzero. When this is the case, the row represents a master file. |
| sys.sysusermsg | Exists in the master database only. Each row represents a user-defined error message. |
| sys.sysprivs | Exists in every database. Contains a row for each database- or server-level permission. Note: Server-level permissions are stored in the master database. |
| sys.sysowners | Exists in every database. Each row represents a database principal. |
| sys.sysobjkeycrypts | Exists in every database. Contains a row for each symmetric key, encryption, or cryptographic property associated with an object. |
| sys.syscerts | Exists in every database. Contains a row for each certificate in a database. |
| sys.sysasymkeys | Exists in every database. Each row represents an asymmetric key. |
| sys.ftinds | Exists in every database. Contains a row for each full-text index in the database. |
| sys.sysxprops | Exists in every database. Contains a row for each extended property. |
| sys.sysallocunits | Exists in every database. Contains a row for each storage allocation unit. |
| sys.sysrowsets | Exists in every database. Contains a row for each partition rowset for an index or a heap. |
| sys.sysrowsetrefs | Exists in every database. Contains a row for each index to rowset reference. |
| sys.syslogshippers | Exists in the master database only. Contains a row for each database mirroring witness. |
| sys.sysremsvcbinds | Exists in every database. Contains a row for each remote service binding. |
| sys.sysconvgroup | Exists in every database. Contains a row for each service instance in Service Broker. |
| sys.sysxmitqueue | Exists in every database. Contains a row for each Service Broker transmission queue. |
| sys.sysdesend | Exists in every database. Contains a row for each sending endpoint of a Service Broker conversation. |
| sys.sysdercv | Exists in every database. Contains a row for each receiving endpoint of a Service Broker conversation. |
| sys.sysendpts | Exists in the master database only. Contains a row for each endpoint created in the server. |
| sys.syswebmethods | Exists in the master database only. Contains a row for each SOAP-method defined on a SOAP-enabled HTTP endpoint that is created in the server. |
| sys.sysqnames | Exists in every database. Contains a row for each namespace or qualified name to a 4-byte ID token. |
| sys.sysxmlcomponent | Exists in every database. Each row represents an XML schema component. |
| sys.sysxmlfacet | Exists in every database. Contains a row for each XML facet (restriction) of XML type definition. |
| sys.sysxmlplacement | Exists in every database. Contains a row for each XML placement for XML components. |
| sys.syssingleobjrefs | Exists in every database. Contains a row for each general N-to-1 reference. |
| sys.sysmultiobjrefs | Exists in every database. Contains a row for each general N-to-N reference. |
| sys.sysobjvalues | Exists in every database. Contains a row for each general value property of an entity. |
| sys.sysguidrefs | Exists in every database. Contains a row for each GUID classified ID reference. |
Updating System Base Tables
You can view the data in the system tables through the system catalog views. To update the metadata in a system base table, use the appropriate Transact-SQL interface (for example, DDL statements). You can't manually update system tables. SQL Server reports the following messages when you perform direct updates to system tables.
A system table is manually updated
Msg 17659: Warning: System table ID <id> has been updated directly in database ID <id> and cache coherence may not have been maintained. SQL Server should be restarted.
Starting a database with a system table that was manually updated
Msg 3859: Warning: The system catalog was updated directly in database ID 17, most recently at date_time.
Executing the DBCC_CHECKDB command after a system table is manually updated
Msg 3859: Warning: The system catalog was updated directly in database ID 17, most recently at date_time.
If you perform manual updates to a system table and encounter a problem, you might be asked to restore from a backup or copy out the data from the affected database to a new database. Learn more about user action error messages.