＝＝＝＝SQL 面试题 ［高手请进］~~＝＝＝＝＝

[mike247]

--------------------------第1题：---------------------------------
表 table1
字段:id int identity(1,1) primary key, name varchar(2)
测试数据：
insert into table1(name)
select 'a' union all
select 'a' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'd'

题目：
删除表中name 重复的字段
结果：
1 a
3 b
4 c
6 d

--------------------------第2题：---------------------------------

表 table2
字段: name varchar(2)
测试数据：
insert into table1(name)
select 'a' union all
select 'a' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'd'
题目：
删除表中name 重复的字段
结果：
1 a
3 b
4 c
6 d


请高手帮忙看看~

[liangCK]

--按某一字段分组取最大(小)值所在行的数据
(爱新觉罗.毓华 2007-10-23于浙江杭州)
/*
数据如下：
name val memo
a    2   a2(a的第二个值)
a    1   a1--a的第一个值
a    3   a3:a的第三个值
b    1   b1--b的第一个值
b    3   b3:b的第三个值
b    2   b2b2b2b2
b    4   b4b4
b    5   b5b5b5b5b5
*/
--创建表并插入数据：
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a',    2,   'a2(a的第二个值)')
insert into tb values('a',    1,   'a1--a的第一个值')
insert into tb values('a',    3,   'a3:a的第三个值')
insert into tb values('b',    1,   'b1--b的第一个值')
insert into tb values('b',    3,   'b3:b的第三个值')
insert into tb values('b',    2,   'b2b2b2b2')
insert into tb values('b',    4,   'b4b4')
insert into tb values('b',    5,   'b5b5b5b5b5')
go

--一、按name分组取val最大的值所在行的数据。
--方法1：
select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name
--方法2：
select a.* from tb a where not exists(select 1 from tb where name = a.name and val > a.val)
--方法3：
select a.* from tb a,(select name,max(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name
--方法4：
select a.* from tb a inner join (select name , max(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name
--方法5
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name
/*
name       val         memo                 
---------- ----------- -------------------- 
a          3           a3:a的第三个值
b          5           b5b5b5b5b5
*/

--二、按name分组取val最小的值所在行的数据。
--方法1：
select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name
--方法2：
select a.* from tb a where not exists(select 1 from tb where name = a.name and val < a.val)
--方法3：
select a.* from tb a,(select name,min(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name
--方法4：
select a.* from tb a inner join (select name , min(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name
--方法5
select a.* from tb a where 1 > (select count(*) from tb where name = a.name and val < a.val) order by a.name
/*
name       val         memo                 
---------- ----------- -------------------- 
a          1           a1--a的第一个值
b          1           b1--b的第一个值
*/

--三、按name分组取第一次出现的行所在的数据。
select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name
/*
name       val         memo                 
---------- ----------- -------------------- 
a          2           a2(a的第二个值)
b          1           b1--b的第一个值
*/

--四、按name分组随机取一条数据。
select a.* from tb a where val = (select top 1 val from tb where name = a.name order by newid()) order by a.name
/*
name       val         memo                 
---------- ----------- -------------------- 
a          1           a1--a的第一个值
b          5           b5b5b5b5b5
*/

--五、按name分组取最小的两个(N个)val
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.val
select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val) order by a.name,a.val
select a.* from tb a where exists (select count(*) from tb where name = a.name and val < a.val having Count(*) < 2) order by a.name
/*
name       val         memo                 
---------- ----------- -------------------- 
a          1           a1--a的第一个值
a          2           a2(a的第二个值)
b          1           b1--b的第一个值
b          2           b2b2b2b2
*/

--六、按name分组取最大的两个(N个)val
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val > a.val ) order by a.name,a.val
select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val desc) order by a.name,a.val
select a.* from tb a where exists (select count(*) from tb where name = a.name and val > a.val having Count(*) < 2) order by a.name
/*
name       val         memo                 
---------- ----------- -------------------- 
a          2           a2(a的第二个值)
a          3           a3:a的第三个值
b          4           b4b4
b          5           b5b5b5b5b5
*/
--七，如果整行数据有重复，所有的列都相同。
/*
数据如下：
name val memo
a    2   a2(a的第二个值)
a    1   a1--a的第一个值
a    1   a1--a的第一个值
a    3   a3:a的第三个值
a    3   a3:a的第三个值
b    1   b1--b的第一个值
b    3   b3:b的第三个值
b    2   b2b2b2b2
b    4   b4b4
b    5   b5b5b5b5b5
*/
--在sql server 2000中只能用一个临时表来解决，生成一个自增列，先对val取最大或最小，然后再通过自增列来取数据。
--创建表并插入数据：
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a',    2,   'a2(a的第二个值)')
insert into tb values('a',    1,   'a1--a的第一个值')
insert into tb values('a',    1,   'a1--a的第一个值')
insert into tb values('a',    3,   'a3:a的第三个值')
insert into tb values('a',    3,   'a3:a的第三个值')
insert into tb values('b',    1,   'b1--b的第一个值')
insert into tb values('b',    3,   'b3:b的第三个值')
insert into tb values('b',    2,   'b2b2b2b2')
insert into tb values('b',    4,   'b4b4')
insert into tb values('b',    5,   'b5b5b5b5b5')
go

select * , px = identity(int,1,1) into tmp from tb

select m.name,m.val,m.memo from
(
  select t.* from tmp t where val = (select min(val) from tmp where name = t.name)
) m where px = (select min(px) from
(
  select t.* from tmp t where val = (select min(val) from tmp where name = t.name)
) n where n.name = m.name)

drop table tb,tmp

/*
name       val         memo
---------- ----------- --------------------
a          1           a1--a的第一个值
b          1           b1--b的第一个值

(2 行受影响)
*/
--在sql server 2005中可以使用row_number函数，不需要使用临时表。
--创建表并插入数据：
create table tb(name varchar(10),val int,memo varchar(20))
insert into tb values('a',    2,   'a2(a的第二个值)')
insert into tb values('a',    1,   'a1--a的第一个值')
insert into tb values('a',    1,   'a1--a的第一个值')
insert into tb values('a',    3,   'a3:a的第三个值')
insert into tb values('a',    3,   'a3:a的第三个值')
insert into tb values('b',    1,   'b1--b的第一个值')
insert into tb values('b',    3,   'b3:b的第三个值')
insert into tb values('b',    2,   'b2b2b2b2')
insert into tb values('b',    4,   'b4b4')
insert into tb values('b',    5,   'b5b5b5b5b5')
go

select m.name,m.val,m.memo from
(
  select * , px = row_number() over(order by name , val) from tb
) m where px = (select min(px) from
(
  select * , px = row_number() over(order by name , val) from tb
) n where n.name = m.name)

drop table tb

/*
name       val         memo
---------- ----------- --------------------
a          1           a1--a的第一个值
b          1           b1--b的第一个值

(2 行受影响)
*/

[liangCK]

select max(id),name
from tb
group by name

[liangCK]

第二题不知说啥.只有一个name字段.
删除重复值..
但又突然id=1,3,4,6出来.

[kk19840210]

create table table1(id int identity(1,1) primary key, name varchar(2))
  insert into table1(name) 
  select 'a' union all 
  select 'a' union all 
  select 'b' union all 
  select 'c' union all 
  select 'c' union all 
  select 'd' 

delete  table1 from table1 a where  exists (select 1 from table1 where name=a.name and id<a.id)

[mike247]

我 刚复制忘了删了

--------------------------第2题：---------------------------------

表 table2
字段: name varchar(2)
测试数据：
insert into table1(name)
select 'a' union all
select 'a' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'd'
题目：
删除表中name 重复的字段
结果：
a
b
c
d

[liangCK]

kk

[liangCK]

select name
from tb
group by name

[liangCK]

这也是面试题?..
感觉像第一天学习SQL应该学的东西.

[kk19840210]

--------------------------第2题：---------------------------------

表 table2
字段: name varchar(2)
测试数据：
insert into table1(name)
select 'a' union all
select 'a' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'd'
题目：
删除表中name 重复的字段
结果：
a
b
c
d

select distinct name into #table1

truncate table table1

insert into table1
select name from #table1

drop table #table1

[mike247]

是啊，我同学的面试题 给我传过了的啊

[mike247]

没别的办法了，，

用一条ＳＱＬ语句　可以吗？

[liangCK]

2005的.

create table table1(name varchar(20))
  insert into table1(name)   
  select 'a' union all   
  select 'a' union all   
  select 'b' union all   
  select 'c' union all   
  select 'c' union all   
  select 'd' 
;
with tmpCTE as
(
  select name,cnt=row_number() over(partition by name order by name)
  from table1
)
delete from tmpCTE where cnt>=2

select * from table1

drop table table1

[chenxin2835]

[Quote=引用 5 楼 kk19840210 的回复:]
SQL code
create table table1(id int identity(1,1) primary key, name varchar(2))
insert into table1(name)
select 'a' union all
select 'a' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'd'

delete table1 from table1 a where exists (select 1 from table1 where name=a.name and id<a.id)
[/Quote]哪位大哥，帮忙解释一下“where exists (select 1 from table1 where name=a.name and id<a.id)”这句啊，小弟看不明白

[mike247]

请高手帮忙看看~

[mike247]

select 1 from table1 where name=a.name and id <a.id

如果 这条语句成立 就删除次行
那个 1 也可以是*
id《a.id 是保留最小的

[Limpire]

--------------------------第1题：---------------------------------
create table #1 (id int identity(1,1) primary key, name varchar(2))
insert into #1(name)
select 'a' union all
select 'a' union all
select 'b' union all
select 'c' union all
select 'c' union all
select 'd'

delete a from #1 a where exists (select 1 from #1 where name=a.name and id<a.id)

select * from #1
/*
删除表中name 重复的字段
结果：
1 a
3 b
4 c
6 d
*/

第二题转换为第一题