T-SQL | 如何在While循环中将值动态设置为变量

Question

I have 12 Variables and all of them have the same SELECT Statement exept for 1 Param. I somehow cant figure out how to so it dynamically.

Here is an example of what I have:

// this here should be dynamic
SET @Var1 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '1')
SET @Var2 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '2')
SET @Var3 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '3')
SET @Var4 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '4')
SET @Var5 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '5')
SET @Var6 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '6')
SET @Var7 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '7')
SET @Var9 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '8')
SET @Var9 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '9')
SET @Var10 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '10')
SET @Var11 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '11')
SET @Var12 = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = '12')    

INSERT INTO VarTable (Var1, Var2, Var3, Var4, Var5, Var6, Var7, Var8, Var9, Var10, Var11, Var12)
    VALUES (@Var1, @Var2, @Var3, @Var4, @Var5, @Var6, @Var7, @Var8, @Var9, @Var10, @Var11, @Var12)

The Table Cols are restricted (no permission to change the table) so I need to assign it like this.

Answer 1

I think you don't need to use variable here :

INSERT INTO VarTable (Var1, Var2, Var3, Var4, Var5, Var6, Var7, Var8, Var9, Var10, Var11, Var12)
      SELECT SUM(CASE WHEN MonthCol = 1 THEN 1 ELSE 0 END), 
             SUM(CASE WHEN MonthCol = 2 THEN 1 ELSE 0 END),
              . . .
             SUM(CASE WHEN MonthCol = 12 THEN 1 ELSE 0 END)
      FROM #TempTable t;

However, here conditional aggregation is enough as there is only 12 months. So, dynamic approach is not needed.

Answer 2

well this is what you can try here:

Declare a table variable with 2 columns

 declare @mytable table(
   VariableName varchar(255),
   VariableValue int
 )

Now Declare 2 more variables, one to set value and second to iterate through loop

 Declare @value int;
 Declare @month int = 1;

Now do the while loop like this:

 while (@month <= 12 ) --since there are only 12 months
 begin
   set @value = (SELECT COUNT(*) FROM #TempTable WHERE MonthCol = cast(@month as varchar));
  insert into  @mytable values ('Month'+cast (@month as varchar), value );
  set @month = @month +1;
 end

Now you'll have your DataSet in table form which you can access by using the simple query:

VariableName   VariableValue   
-----------    -------------- 
   Month1          23
   Month2          19
   Month3          66
   Month4          12
   Month5          05
   Month6          04
   Month7          63    
   Month8          76    
   Month9          21    
   Month10         23    
   Month11         63    
   Month12         12  



Select * from @mytable where VariableName = 'Month1' 

Answer 3

This looks like it should be a PIVOT :

INSERT INTO VarTable (Var1, Var2, Var3, Var4, Var5, Var6, Var7, Var8, Var9, Var10, Var11, Var12)
SELECT [1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12]
FROM (select MonthCol,COUNT(*) Cnt from #TempTable group by MonthCol) t
PIVOT (SUM(Cnt) FOR MonthCol IN ([1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12])) u

I believe we have to "pre-aggregate" the data in a subquery because COUNT(*) isn't allowed in the PIVOT clause ¹ . Note that each MonthCol will have a single Cnt value so we could use any aggregate in the PIVOT that returns a single input unaltered - SUM , MIN or MAX . I arbitrarily picked SUM above.

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¹ You have to supply specific column(s) to the aggregate.