Loop through a table using Cross apply and UNION ALL the results

问题

Trying to write a query which will behave like a foreach

Query :

select label ,NTILE(10) over(order by label ASC) Quartile INTO #labelTempTab from dbo.ReportFieldsLookup

The data will be like :

label   Quartile
-----   --------
la1         1
la2         1
la3         1
sa1         2
sa2         2
sq3         2
ha1         3
ha2         3
ha3         3
ka1         4
ka2         4
kas3        4

Continuation of Query :

DECLARE @sql nvarchar(max)

SELECT * INTO #SetValuesTable  FROM svo_tbl

SET @sql = 'SELECT MNUM, Label , LabelValue ,[Property Type] FROM #SetValuesTable '
              +' CROSS APPLY ( VALUES '
              +  stuff(( SELECT ',('''+ replace(C.label,'''','"') + ''',' + quotename(C.label) + ')'   FROM #labelTempTab c WHERE c.Quartile = 1 group by label FOR xml path('')), 1, 1, '')
              +' ) AS UPTab (Label , LabelValue);'

EXEC(@sql)

The above query will unpivot only for Quartile = 1 How can i make it work for 1 to n and union all the results.

data in #SetValuesTable will look like :

MNUM      la1   la2     la3   sa1  sa2      sq3    ha1     ha2    ha3   ka1   ka2 Property Type 
12         1     0      2      1    0       8       3       4      0     1     2    s
13         4     0      5      1    6       8       5       2      1     1     3    p

The result(Expected output) should look like

MNUM  Label LabelValue Property Type
12     la1     1          s
12     la2     0          s
12     la3     2          s
12     sa1     1          s
12     sa2     0          s
12     sa3     8          s

........

13     ka1     1          p
13     ka2     1          p
12     ka3     3          p

continuation of the query :

SET @sql = @sql + ' INNER JOIN dbo.ReportFieldsLookup tt ON tt.label = Label'
SET @sql = @sql + 'INNER JOIN dbo.SplitStrings_Ordered('''''09-404811,10-433495,10-433575,10-423789'''', ',') AS s ON #SetValuesTable.MNum = s.MNum ORDER BY s.[Index];

The above two statements are taking long time. Especially the Last inner join which is for sorting is taking long time. I think using cross apply might greatly reduce the execution time.

回答1:

Use Cross Apply to unpivot the result. Dynamic query query should be constructed in this format.

SELECT mnum,
       label,
       label_value,
       [Property Type]
FROM   #SetValuesTable
       CROSS apply(VALUES ('la1',la1),('la2',la2),('la3',la3),
                          ('sa1',sa1),('sa2',sa2),('sa3',sa3),
                          ('ha1',ha1),('ha2',ha2),('ha3',ha3),
                          ('ka1',ka1),('ka2',ka2)) cs (label, label_value)

Dynamic query should be something like

DECLARE @label VARCHAR(max)='',
        @sql   NVARCHAR(max)

SELECT @label += '(' + '''' + label + ''',' + label + '),'
FROM   (SELECT DISTINCT Isnull(label, '') label
        FROM   #labelTempTab)a

SELECT @label = LEFT(@label, Len(@label) - 1)

SET @sql= 'SELECT mnum,
             label,
             label_value,
             [Property Type]
    FROM   #SetValuesTable
           CROSS apply(VALUES ' + @label
          + ') cs (label, label_value) '

EXEC Sp_executesql @sql

Note : Since you are generating values list from #labelTempTab table make sure you have all the labels present in #SetValuesTable table

来源：https://stackoverflow.com/questions/28160637/loop-through-a-table-using-cross-apply-and-union-all-the-results

标签

sql

sql-server

sql-server-2012

unpivot

cross-apply