sql中的不常见查询

1.对于CROSS APPLY 和 OUTER APPLY 的应用：

CROSS APPLY 类似于INNER JOIN 但是，可以规定对于满足条件的数据需要关联几行，应用场景: 每个零件把第一个工单关联出来；

OUTER APPLY 类似于LEFT JOIN ,不同之处同上；

--inner join 

SELECT a.part_no,b.workorder FROM dbo.sys_part a INNER JOIN dbo.g_workorder_detail b ON a.part_id =b.part_id 

---执行结果：

part_no   workorder
1144514
1912900
1912900
1912900
1912900
1912900
1144514

---cross apply 

SELECT a.part_no,c.workorder FROM dbo.sys_part a CROSS APPLY
(SELECT TOP 1 * FROM dbo.g_workorder_detail b WHERE a.part_id =b.part_id ORDER BY b.workorder_id) AS c

执行结果:

part_no workorder
1144514
1912900

---outer apply 

SELECT a.part_no,c.workorder FROM sys_part a OUTER APPLY
(SELECT TOP 1 * FROM dbo.g_workorder_detail b WHERE a.part_id =b.part_id ORDER BY b.workorder_id) AS c

---执行结果:

part_no workorder

90740 NULL

90789 NULL
369832 NULL
507994 NULL

2.SQL语句执行结果增加列显示:

--其中对于over之后的排序为整个语句显示信息的排序

 SELECT TOP 5 ROW_NUMBER() OVER(ORDER BY part_id) AS row_id ,part_no  FROM sys_part 

3.SQL语句对于锁表的查询：

SELECT b.name AS [database], a.spid, a.blocked, a.waittime / 1000 AS wait_time, a.loginame,CONVERT(VARCHAR(50),login_time,120) login_time,
CONVERT(VARCHAR(50),last_batch,120) last_batch, open_tran, a.status, hostname, program_name, cmd
FROM sys.sysprocesses a
JOIN sys.sysdatabases b ON a.dbid = b.dbid
WHERE spid IN ( SELECT blocked
FROM sys.sysprocesses
WHERE blocked > 0 AND spid != blocked )
UNION
SELECT b.name AS [database], a.spid, a.blocked, a.waittime / 1000 AS wait_time,a.loginame, CONVERT(VARCHAR(50),login_time,120) login_time,
CONVERT(VARCHAR(50),last_batch,120) last_batch, open_tran, a.status, hostname, program_name, cmd
FROM sys.sysprocesses a
JOIN sys.sysdatabases b ON a.dbid = b.dbid
WHERE blocked > 0 AND waittime >0 AND spid != blocked
ORDER BY spid

--对于得到的具体spid可以根据语句来得到具体的sql语句： DBCC INPUTBUFFER(SPID)

4.SQL中对于登录信息的获取：

SELECT
s.[host_name],
con.client_net_address,
s.login_name,
s.[program_name]
FROM sys.dm_exec_connections AS con INNER JOIN sys.dm_exec_sessions AS s
ON con.session_id=s.session_id AND s.session_id=@@SPID  ---当前执行此内容的SPID

5.对于表碎片的查看，决定是否要重建索引：

DBCC SHOWCONTIG(sys_part)

---显示结果：

DBCC SHOWCONTIG scanning 'sys_part' table...
Table: 'sys_part' (308912172); index ID: 0, database ID: 46
TABLE level scan performed.
- Pages Scanned................................: 276
- Extents Scanned..............................: 39
- Extent Switches..............................: 38
- Avg. Pages per Extent........................: 7.1
- Scan Density [Best Count:Actual Count].......: 89.74% [35:39] ---此百分比越大越好
- Extent Scan Fragmentation ...................: 33.33%  ---扩展盘区扫描碎片，越小越好
- Avg. Bytes Free per Page.....................: 2542.0
- Avg. Page Density (full).....................: 68.59%  ------------每叶的密度 --此值太低，就得考虑索引重建
DBCC execution completed. If DBCC printed error messages, contact your system administrator.

---如需要重建索引，可执行： DBCC DBREINDEX(sys_part) 

6.对于JOB 方面的查询，归属，及其执行的内容 

---对于Job是归属那个账号 在执行的查询
SELECT a.name AS job_name,b.loginname,a.date_created AS job_createtime,a.date_modified AS jobmodifytime
FROM msdb.dbo.sysjobs a INNER JOIN master.dbo.syslogins b ON a.owner_sid =SUSER_SID(B.loginname)
WHERE 1=1
AND A.enabled =1 --表示启用的JOB
AND B.loginname='sa' --账号
ORDER BY a.job_id

--关于在运行中的job执行的语句

SELECT a.name AS job_name,b.step_name,b.database_name,b.step_id,b.command
FROM msdb.dbo.sysjobs a INNER JOIN msdb.dbo.sysjobsteps b ON a.job_id=b.job_id
WHERE 1=1
AND a.enabled =1
ORDER BY a.job_id,b.step_id