What is the DBCC command and why it is used?

The Database-Consistency-Checker(DBCC) will help us to check the consistency of the database, this is also known as database console commands.

• Maintenance
• Miscellaneous
• Informational
• Validation 

DBCC HELP

This command falls under the Miscellaneous category.

Syntax

DBCC HELP ('?'); 

The Maintenance   

Into this category includes commands for the tasks related to database, index, and filegroup, as shown below.

• CLEANTABLE
• DBREINDEX
• DROPCLEANBUFFERS
• FREEPROCCACHE
• INDEXDEFRAG,
• SHRINKDATABASE
• SHRINKFILE
• UPDATEUSAGE

The Miscellaneous   

Into this category includes commands for the tasks related to trace flag or DDL memory management, as shown below.

• HELP
• FLUSHAUTHCACHE
• TRACEOFF
• FREESESSIONCACHE
• TRACEON
• FREESYSTEMCACHE
• CLONEDATABASE  

The Informational

Into this category includes commands for tasks to collect or display different types of information, like below.

• INPUTBUFFER
• SHOWCONTIG
• OPENTRAN
• OUTPUTBUFFER
• PROCCACHE
• SHOW_STATISTICS
• SQLPERF
• TRACESTATUS
• USEROPTIONS

The Validation

Inti this category includes commands for the tasks to perform some kind of validation actions on the database, index, tables, etc., which I would say are more useful in certain ways, like below.

• CHECKALLOC
• CHECKCATALOG
• CHECKCONSTRAINTS
• CHECKDB
• CHECKFILEGROUP
• CHECKIDENT
• CHECKTABLE