本教程涵盖了SQL语言中常用的全面命令和语句，帮助用户掌握数据库查询、数据操作及管理技巧。
SQL中最常用的查询命令包括：查看某个数据库的连接数可以使用`SELECT COUNT(*) FROM Master.dbo.SysProcesses WHERE dbid=db_id()`；前10名其他等待类型可以通过执行`SELECT TOP 10 * from sys.dm_os_wait_stats ORDER BY wait_time_ms DESC`来获取，同时也可以通过筛选特定类型的等待事件如PAGELATCH或LAZYWRITER_SLEEP使用命令`SELECT *FROM sys.dm_os_wait_stats WHERE wait_type like PAGELATCH% OR wait_type like LAZYWRITER_SLEEP%`; 监控CPU压力可以利用查询语句 `SELECT scheduler_id, current_tasks_count, runnable_tasks_count FROM sys.dm_os_schedulersWHERE scheduler_id < 255`；展示最差的前10名使用查询可以通过执行以下命令来实现：`SELECT TOP 10 ProcedureName = t.text, ExecutionCount = s.execution_count,AvgExecutionTime = isnull ( s.total_elapsed_time / s.execution_count, 0 ), AvgWorkerTime = s.total_worker_time / s.execution_count, TotalWorkerTime = s.total_worker_time, MaxLogicalReads = s.max_logical_reads,MaxPhysicalReads = s.max_physical_reads, MaxLogicalWrites = s.max_logical_writes,CreationDateTime = s.creation_time,CallsPerSecond = isnull ( s.execution_count / datediff ( second , s.creation_time, getdate ()), 0 ) FROM sys.dm_exec_query_stats AS s CROSS APPLY sys.dm_exec_sql_text( s.sql_handle ) AS t ORDER BY s.max_physical_reads DESC`；查询总信号等待时间、资源的等待时间和对应的百分比使用 `SELECT SUM(signal_wait_time_ms) AS total_signal_wait_time_ms, SUM(wait_time_ms - signal_wait_time_ms) AS resource_wait_time_ms,SUM(signal_wait_time_ms) * 1.0 / SUM (wait_time_ms) * 100 AS [signal_wait_percent],SUM(wait_time_ms - signal_wait_time_ms) * 1.0 / SUM (wait_time_ms) * 100 AS [resource_wait_percent]FROM sys.dm_os_wait_stats`; 查看进程所执行的SQL语句可以使用`IF (SELECT COUNT(*) FROM master.dbo.sysprocesses) > 500 BEGIN SELECT text, CROSS APPLY master.sys.dm_exec_sql_text(a.sql_handle) FROM master.sys.sysprocesses AS a END`；获取活动会话详情和释放空连接则需要通过特定的条件筛选并执行如 `spid> 50 and waittype = 0x0000 and waittime = 0 and status = sleeping and last_batch < dateadd(minute, -10, getdate())` 的查询语句；查看当前占用 CPU 资源最高的会话和其中执行的语句可以使用 `SELECT spid, cmd, cpu, physical_io, memusage,(select top 1 [text] from ::fn_get_sql(sql_handle)) sql_text FROM master..sysprocesses ORDER BY cpu desc,physical_io desc`；查询缓存中重用次数少，占用内存大的查询语句可以使用 `SELECT TOP 100 usecounts,objtype,p.size_in_bytes,[sql].[text] FROM sys.dm_exec_cached_plans AS p OUTER APPLY sys.dm_exec_sql_text (p.plan_handle) AS sql ORDER BY usecounts, p.size_in_bytes desc`；统计总的CPU时间可以通过执行命令：`SELECT top 50 qt.text AS SQL_text ,SUM(qs.total_worker_time) AS total_cpu_time,SUM(qs.execution_count) AS total_execution_count,SUM(qs.total_worker_time)/SUM(qs.execution_count) AS avg_cpu_time,COUNT(*) AS number_of_statements FROM sys.dm_exec_query_stats qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) as qt GROUP BY qt.text ORDER BY total_cpu_time DESC`。这些命令和查询语句可以有效地帮助管理和优化数据库性能，同时也能及时发现并解决潜在的问题。此外，还可以通过计算可运行状态下的工作进程数量来进一步了解系统负载情况：`SELECT COUNT(*) AS workers_waiting_for_cpu, s.scheduler_id FROM sys.dm_os_workers AS o INNER JOIN sys.dm_os_schedulers AS s ON o.scheduler_address=s.scheduler_address AND s.scheduler_id<255 WHERE o.state=RUNNABLE GROUP BY s.scheduler_id`. 这些查询可以为数据库管理员提供重要的性能监控和优化依据。
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