面试sql题目总结

sql经典面试题

group by

create table teacher(teacher nvarchar(10),teach_day int,teach_desc nchar(1));

insert into teacher values('老师1',2,'有')
insert into teacher values('老师1',3,'有')
insert into teacher values('老师1',3,'有')
insert into teacher values('老师2',2,'无')
insert into teacher values('老师2',2,'有')
insert into teacher values('老师2',1,'有')
insert into teacher values('老师3',1,'有')
insert into teacher values('老师3',3,'无')

teacher     teach_day    teach_desc
老师1         2               有
老师1         3               有
老师1         3               有
老师2         2               无
老师2         2               有
老师2         1               有
老师3         1               有
老师3         3               无

Result:
teacher    monday   tuesday     wednesday
老师1         0       1            2 
老师2         1       1            0 
老师3         1       0            0 


select teacher,
sum(case when teach_day=1 then 1 else 0 end)'monday',
sum(case when teach_day=2 then 1 else 0 end)'tuesday',
sum(case when teach_day=3 then 1 else 0 end)'wednesday'
from teacher where teach_desc='有' group by teacher

Linq:
from t in Teachers
where t.Teach_desc=='有'
group t by t.Content into g
select new{
    teacher=g.Key,
    monday=g.Sum(s=>s.Teach_day==1?1:0),
    tuesday=g.Sum(s=>s.Teach_day==2?1:0),
    wednesday=g.Sum(s=>s.Teach_day==3?1:0)
}

对年月日分组查询,统计每月每天每年的活跃人数,根据登陆日期

create table  logininfo(name varchar(50),logindate datetime)

insert into logininfo values('dnadan',getdate())
insert into logininfo values('c','2017/9/21 7:58:05')
insert into logininfo values('d','2017/9/20 0:58:05')
insert into logininfo values('c','2017/9/21 10:58:05')
insert into logininfo values('d','2017/9/20 12:58:05')
insert into logininfo values('e','2017/9/19 23:58:05')
insert into logininfo values('f','2017/9/20 20:58:05')
insert into logininfo values('g','2017/9/21 20:58:05')
insert into logininfo values('h','2015/9/19 20:58:05')
insert into logininfo values('i','2014/9/20 20:58:05')
insert into logininfo values('j','2016/9/21 20:58:05')


统计每天的登陆人数
select convert(date,logindate)date,count(*) from logininfo group by convert(date,logindate); 

Linq:

from l in Logininfos 
group l by l.Logindate.Value.Date into g
select new{date=g.Key,sum=g.Count()}


统计每月登陆人数
select convert(varchar(7),logindate,126),count(*) from logininfo group by convert(varchar(7),logindate,126)

Linq:
from l in Logininfos
group l by l.Logindate.Value.Year+"/"+(l.Logindate.Value.Month<10?"0":"")+l.Logindate.Value.Month into g
select new{date=g.Key,sum=g.Count()}

这里应该使用拼接,这样可以减少对子查询的嵌套查询

临时表和全局临时表

5.在sqlserver2000中请用sql创建一张用户临时表和系统临时表，里面包含两个字段ID和IDValues,类型都是int型，并解释下两者的区别?
------------------------------------------
用户临时表:create table #xx(ID int, IDValues int)
系统临时表:create table ##xx(ID int, IDValues int)

区别:
用户临时表只对创建这个表的用户的Session可见,对其他进程是不可见的.
当创建它的进程消失时这个临时表就自动删除.

全局临时表对整个SQL Server实例都可见,但是所有访问它的Session都消失的时候,它也自动删除.

使用Left Join 拼接出结果

    dept_yeji
    mon         dep     yj
    -------------------------------
    一月份      01      10
    一月份      02      10
    一月份      03      5
    二月份      02      8
    二月份      04      9
    三月份      03      8

    dept

    dep      dname
    --------------------------------
    01      国内业务一部
    02      国内业务二部
    03      国内业务三部
    04      国际业务部

    result

    dep     一月份      二月份      三月份
    --------------------------------------
    01      10           null          null
    02      10           8             null
    03      5             null          8
    04      null          9             null

    create table dept_yeji(mon varchar(10),dep varchar(2),yj int)
    create table dept(dep varchar(2),dname varchar(20))

    insert into dept_yeji values('一月份','01',10)
    insert into dept_yeji values('一月份','02',10)
    insert into dept_yeji values('一月份','03',5)
    insert into dept_yeji values('二月份','02',8)
    insert into dept_yeji values('二月份','04',9)
    insert into dept_yeji values('三月份','03',8)

    insert into dept values('01','国内业务一部')
    insert into dept values('02','国内业务二部')
    insert into dept values('03','国内业务三部')
    insert into dept values('04','国内业务部')
    
    
    
    select a.dep,b.yj '一月份',c.yj '二月份',d.yj '三月份'
    from dept a
    left join dept_yeji b on a.dep=b.dep and b.mon='一月份'
    left join dept_yeji c on a.dep=c.dep and c.mon='二月份'
    left join dept_yeji d on a.dep=d.dep and d.mon='三月份' 



    Linq:

    from a in Depts
    join b in Dept_yejis on new{a.Dep,Mon="一月份"} equals new{b.Dep,b.Mon} into bs
    from b in bs.DefaultIfEmpty()
    join c in Dept_yejis on new{a.Dep,Mon="二月份"} equals new{c.Dep,c.Mon} into cs
    from c in cs.DefaultIfEmpty()
    join d in Dept_yejis on new{a.Dep,Mon="三月份"} equals new{d.Dep,d.Mon} into ds
    from d in ds.DefaultIfEmpty()
    select new{
        a.Dep,
        first=b.Yj,
        second=c.Yj,
        thired=d.Yj
    }

综合使用

    payrec

    fcr_id    fcr_date           rank     fcr_busType  fcr_curr fcr_amount     
    1	2016-03-22 00:00:00.000	销售家具	收	cny	720
    2	2015-01-12 00:00:00.000	销售家具	收	cny	12090
    3	2015-01-12 00:00:00.000	支付房租	付	cny	-9091
    4	2015-01-12 00:00:00.000	红星转账	收	cny	100000
    5	2015-01-12 00:00:00.000	购买家具100件	付	cny	-10918
    6	2015-01-12 00:00:00.000	购买家具30件	付	cny	-4069
    7	2015-01-14 00:00:00.000	购买家具150件	付	cny	-20884
    8	2015-01-14 11:00:00.000	购买家具100件	付	cny	-10394
    9	2015-01-14 10:00:00.000	销售家具	收	cny	39800
    10	2015-01-14 00:00:00.000	支付欠款	付	cny	-8800
    11	2015-01-14 00:00:00.000	支付欠款	付	cny	-40000
    12	2015-01-15 00:00:00.000	红星转账	收	cny	710
    13	2015-01-15 00:00:00.000	红星转账	收	cny	810
    14	2015-01-15 00:00:00.000	红星转账	收	cny	13010
    15	2015-01-15 00:00:00.000	红星转账	收	cny	3800
    
    
    统计结果

    1	2015-01-12 00:00:00.000	     12090		12090
    2	2015-01-12 00:00:00.000		     -9091	2999
    3	2015-01-12 00:00:00.000	    100000		102999
    4	2015-01-12 00:00:00.000		    -10918	92081
    5	2015-01-12 00:00:00.000		     -4069	88012
    6	2015-01-14 00:00:00.000		    -20884	67128
    7	2015-01-14 00:00:00.000		     -8800	58328
    8	2015-01-14 00:00:00.000		    -40000	18328
    9	2015-01-14 10:00:00.000	     39800		58128
    10	2015-01-14 11:00:00.000		    -10394	47734
    11	2015-01-15 00:00:00.000	       710		48444
    12	2015-01-15 00:00:00.000	       810		49254
    13	2015-01-15 00:00:00.000	     13010		62264
    14	2015-01-15 00:00:00.000	      3800		66064
    15	2016-03-22 00:00:00.000	       720		66784
    
    
    
    
    需要使用到临时表 和 row_num() over (order by xxx) 和 case when

    create table payrec(
        fcr_id int identity(1,1),
        fcr_date datetime,
        fcr_remark varchar(20),
        fcr_busType varchar(2),
        fcr_curr varchar(5),
        fcr_amount decimal
    )
    
    insert into payrec values 
    ('2016/3/22','销售家具','收','cny',720), -- 这里故意放了一条时间靠后的记录在这里,是为了用fcr_date来排序,可以用临时表先排序
    ('2015/1/12','销售家具','收','cny',12090),
    ('2015/1/12','支付房租','付','cny',-9090.84),
    ('2015/1/12','红星转账','收','cny',100000),
    ('2015/1/12','购买家具100件','付','cny',-10917.68),
    ('2015/1/12','购买家具30件','付','cny',-4069.22),
    ('2015/1/14','购买家具150件','付','cny',-20883.55),
    ('2015/1/14 11:00','购买家具100件','付','cny',-10394.44),
    ('2015/1/14 10:00','销售家具','收','cny',39800),
    ('2015/1/14','支付欠款','付','cny',-8800),
    ('2015/1/14','支付欠款','付','cny',-40000),
    ('2015/1/15','红星转账','收','cny',710),
    ('2015/1/15','红星转账','收','cny',810),
    ('2015/1/15','红星转账','收','cny',13010),
    ('2015/1/15','红星转账','收','cny',3800)



    create procedure query_fcr
    as
    begin
        select rowid=row_number() over (order by fcr_date),* into #payrec from payrec ; -- 临时表存储排序结果

        select rowid,fcr_date ,
        (case when fcr_amount >0 then str(fcr_amount) else '' end) '收',
        (case when fcr_amount<0 then str(fcr_amount) else '' end) '付', 
        '余额'=(select sum(fcr_amount) from #payrec where rowid<=a.rowid) from #payrec a
    end


    select * from payrec
    exec query_fcr