Some Simple Queries That Might Be Helpful

Here are some simple queries that might be helpful for you.

To check number of open connection in SQL server: 

SELECT DB_NAME(dbid) AS DBName, COUNT(dbid) AS NumberOfConnections, loginame AS LoginName
FROM sys.sysprocesses
WHERE dbid > 0
GROUP BY dbid, loginame;

To check the number of queries running currently on your server:

SELECT sqltext.TEXT, req.session_id, req.STATUS, req.command, req.cpu_time, req.total_elapsed_time
FROM sys.dm_exec_requests REQ
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS sqltext;

Find all dependencies of a table in Sql server 

SELECT referencing_schema_name, referencing_entity_name, referencing_id, referencing_class_desc
FROM sys.dm_sql_referencing_entities('dbo.Clients', 'OBJECT');

Shows all the sessions that are currently established in Sql server. 

EXEC sp_who2

//Or

EXEC sp_who

Shows all ACTIVE sessions that are currently established in SQL server. 

EXEC sp_who 'Active'

//Or

EXEC sp_who2 'Active'