Question

我正在尝试动态转换这样的表：

router.get('/', function(req, res, next) {
   res.send('index');
});

进入类似的事情：

+----+---------+-------+
| ID | Subject | Users |
+----+---------+-------+
|  1 | Hi!     | Anna  |
|  2 | Hi!     | Peter |
|  3 | Try     | Jan   |
|  4 | Try     | Peter |
|  5 | Try     | Jan   |
|  6 | Problem | Anna  |
|  7 | Problem | José  |
|  8 | Test    | John  |
|  9 | Test    | John  |
| 10 | Hi!     | Anna  |
| 11 | Hi!     | José  |
| 12 | Hi!     | Anna  |
| 13 | Hi!     | Joe   |
+----+---------+-------+

我一直在阅读以下链接，但我们考虑将列拆分为预定数量的列：

Splitting SQL Columns into Multiple Columns Based on Specific Column Value

Split column into two columns based on type code in third column

我需要根据表格的内容将其拆分。

Answer 1

SQL：

--【Build Test Data】
create table #Tem_Table ([ID] int,[Subject] nvarchar(20),[Users] nvarchar(20));
insert into #Tem_Table ([ID],[Subject] ,[Users]) values 
    ('1','Hi!','Anna')
    ,('2','Hi!','Peter')  
    ,('3','Try','Jan')  
    ,('4','Try','Peter')  
    ,('5','Try','Jan')  
    ,('6','Problem','Anna')  
    ,('7','Problem','José')  
    ,('7','Test','John')  
    ,('9','Test','John') 
    ,('10','Hi! ','Anna')  
    ,('11','Hi! ','José')  
    ,('12','Hi! ','Anna')  
    ,('13','Hi! ','Joe')   
;

--STEP 1 distinct and ROW_NUMBER
with distinct_table as (
    select  [Subject],[Users]
    ,ROW_NUMBER() OVER (PARTITION BY [Subject] order by [Users]) [rank]
    from (
        select distinct [Subject],[Users] from #Tem_Table
    ) T00
)
--STEP 2 Group by row_count
,group_table as (
    select [Subject] 
    from distinct_table T
    group by [Subject]
)
--STEP 3 Use Left Join and Rank
select 
    T.[Subject],T1.[Users] as User1, T2.[Users] as User2 , T3.[Users] as User3, T4.[Users] as User4
from group_table T
left join distinct_table T1 on T.[Subject] = T1.[Subject] and T1.[rank] = 1
left join distinct_table T2 on T.[Subject] = T2.[Subject] and T2.[rank] = 2
left join distinct_table T3 on T.[Subject] = T3.[Subject] and T3.[rank] = 3
left join distinct_table T4 on T.[Subject] = T4.[Subject] and T4.[rank] = 4
order by [Subject];

结果：

-------------------- -------------------- -------------------- -------------------- --------------------
Hi!                  Anna                 Joe                  José                 Peter
Problem              Anna                 José                 NULL                 NULL
Test                 John                 NULL                 NULL                 NULL
Try                  Jan                  Peter                NULL                 NULL

更新动态版本：

--STEP 1 distinct and ROW_NUMBER
SELECT * into #distinct_table from (
    select  [Subject],[Users]
    ,ROW_NUMBER() OVER (PARTITION BY [Subject] order by [Users]) [rank]
    from (
        select distinct [Subject],[Users] from #Tem_Table
    ) T00    
)T;

--STEP 2 Group by row_count
SELECT * into #group_table from (
    select [Subject] ,count(1) [count]
    from #distinct_table T
    group by [Subject]  
)T;


--Use Exec
DECLARE @select_sql AS NVARCHAR(MAX) = ' select  T.[Subject] ',
@join_sql AS NVARCHAR(MAX) = ' from #group_table T ',
@max_count INT = (SELECT max([count]) FROM #group_table),
@temp_string NVARCHAR(5),
@temp_string_addone NVARCHAR(5)
;

DECLARE @index int = 0 ;
WHILE @index < @max_count
BEGIN
    sELECT @temp_string = Convert(nvarchar(10),@index);
   sELECT @temp_string_addone = Convert(nvarchar(10),@index+1);
   select  @select_sql = @select_sql + ' , T'+@temp_string_addone+'.[Users] as User'+@temp_string_addone+' '
   select  @join_sql = @join_sql + 'left join #distinct_table T'+@temp_string_addone+' on T.[Subject] = T'+@temp_string_addone+'.[Subject] and T'+@temp_string_addone+'.[rank] = '+@temp_string_addone+' ';
   SET @index = @index + 1;
END;

EXEC (@select_sql
+ @join_sql
+' order by [Subject]; ')
;

Answer 2

CREATE TABLE mytable
    ([ID] int, [Subject] varchar(7), [Users] varchar(5))
;

INSERT INTO mytable
    ([ID], [Subject], [Users])
VALUES
    (1, 'Hi!', 'Anna'),
    (2, 'Hi!', 'Peter'),
    (3, 'Try', 'Jan'),
    (4, 'Try', 'Peter'),
    (5, 'Try', 'Jan'),
    (6, 'Problem', 'Anna'),
    (7, 'Problem', 'José'),
    (8, 'Test', 'John'),
    (9, 'Test', 'John'),
    (10, 'Hi!', 'Anna'),
    (11, 'Hi!', 'José'),
    (12, 'Hi!', 'Anna'),
    (13, 'Hi!', 'Joe')
;


select distinct subject,
(select  users from  (
select  distinct users from mytable where subject=m.subject) a order by users offset 0 rows fetch next 1 row only) user1,
(select  users from  (
select  distinct users from mytable where subject=m.subject) a order by users offset 1 rows fetch next 1 row only) user2,
(select  users from  (
select  distinct users from mytable where subject=m.subject) a order by users offset 2 rows fetch next 1 row only) user3,
(select  users from  (
select  distinct users from mytable where subject=m.subject) a order by users offset 3 rows fetch next 1 row only) user4

from mytable m

Answer 3

您可以使用以下动态查询来获取结果 -

create table test_Raw(ID int ,Subject varchar(100), Users varchar(100))

insert into test_Raw
values (1,' Hi!','Anna'),
(2,' Hi!','Peter'),
(3,'Try','Jan'),
(4,'Try','Peter'),
(5,'Try','Jan'),
(6,'Problem','Anna'),
(7,'Problem','José'),
(8,'Test','John'),
(9,'Test','John'),
(10,' Hi!','Anna'),
(11,' Hi!','José'),
(12,' Hi!','Anna'),
(13,' Hi!','Joe')

--select * from test_Raw

select   dense_RANK() over( order by Subject) Ranking1,  dense_RANK()     over(partition by Subject order by users) Ranking2 , Subject , Users  
into test 
from test_Raw
group by Subject , Users
order by 3

declare @min int , @mx int , @Select nvarchar(max) , @from nvarchar(max) ,     @vmin varchar(3) 

select @min= 1 , @mx = MAX(Ranking2) , @Select=  'select ' , @from = ' from     test t1 ' , @vmin = '' from test


while  (@min<=@mx)
begin
    select @vmin = CAST(@min as varchar(3))
    select @Select = @Select +  CASE WHEN @min = 1 THEN  't1.Ranking1 as ID     , t1.Subject  , t1.Users AS User1 ' ELSE ',t' +@vmin+'.Users as User'+@vmin  END 
    select @from = @from  +  CASE WHEN @min = 1 THEN  '' ELSE ' left join     test t'+@vmin + ' on t1.Ranking1 = t' + @vmin + '.Ranking1 and t1.Ranking2 + ' +     cast (@min-1 as varchar(10)) + ' = t'+@vmin+'.Ranking2'  END 
    set @min = @min + 1
end 

select @Select = @Select +  @from + ' where  t1.Ranking2 = 1'

exec sp_executesql @Select

根据不同的列值将SQL列动态拆分为多个列

3 个答案:

SQL：

结果：

更新动态版本：