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1、查询某一个表中按照某一个字段分组排序，获得每一组的序号及详细业务信息
如: 查询儿童体检表中每一个人的历次检查记录，按照检查日期排序分组
select grbjh,row_number() over (partition by grbjh order by TJRQ) as id,TJRQ,*
from eb_jc_tgjc
如需要获取末次检查记录，可套用一层子查询来实现
select grbjh,TJRQ as MCTJRQ
from
(
select grbjh,row_number() over (partition by grbjh order by TJRQ DESC) as id,TJRQ
from eb_jc_tgjc
) a where id = 1
2、行列转换，用于将横表数据转换为纵表数据
如：成绩表中记录了学生的每一门课的记录，需要转换为一个学生各项成绩的纵表
传统写法：
select id,
max(case when kcdm = 'yw' then fs else null end) as '语文',
max(case when kcdm = 'sx' then fs else null end) as '数学',
max(case when kcdm = 'yy' then fs else null end) as '英语'
from cjb
group by id
使用sqlserver自带函数：
3、查询数据库耗时严重语句
SELECT
(total_elapsed_time / execution_count)/1000 N'平均时间ms'
,total_elapsed_time/1000 N'总花费时间ms'
,total_worker_time/1000 N'所用的CPU总时间ms'
,total_physical_reads N'物理读取总次数'
,total_logical_reads/execution_count N'每次逻辑读次数'
,total_logical_reads N'逻辑读取总次数'
,total_logical_writes N'逻辑写入总次数'
,execution_count N'执行次数'
,SUBSTRING(st.text, (qs.statement_start_offset/2) + 1,
((CASE statement_end_offset
WHEN -1 THEN DATALENGTH(st.text)
ELSE qs.statement_end_offset END
- qs.statement_start_offset)/2) + 1) N'执行语句'
,creation_time N'语句编译时间'
,last_execution_time N'上次执行时间'
FROM
sys.dm_exec_query_stats AS qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) st
WHERE
SUBSTRING(st.text, (qs.statement_start_offset/2) + 1,
((CASE statement_end_offset
WHEN -1 THEN DATALENGTH(st.text)
ELSE qs.statement_end_offset END
- qs.statement_start_offset)/2) + 1) not like 'tch%'
ORDER BY
total_elapsed_time / execution_count DESC;
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