Is there a way to split the results of a select query into two equal halfs?

Question

I need a solution for a select query in Sql Server 2005.

I\'d like to have a query returning two ResultSets each of which holding exactly half of all records matchin

Answer 1

If this is SQL Server 2000, then I'd be inclined to find the PK of the middle value like so:

Declare @MiddleId int

Set @MiddleId = (
                Select TOP 1 PK
                From (
                        Select TOP 50 PERCENT PK
                        From Table
                        Order By TheId ASC
                        )
                Order By TheId DESC
                )

Select ...
From Table
Where TheId <= @MiddleId

Select ..
From Table
Where TheId > @MiddleId

With SQL Server 2005, I'd be inclined to do the same but you can use a CTE

;With NumProjects As
    (
    Select Id, ROW_NUMBER() OVER (ORDER BY TheId ASC ) As Num
    From Table
    )
Select @MiddleId = Id
From Table
Where Num = CEILING( (Select Count(*) From Table) / 2 )

Answer 2

SQL Server 2005 and similar:

select *, ntile(2) over(order by theid) as tile_nr from thetable

ntile(n) allocates the output into n segments, each of the same size (give or take rounding when the number of rows isn't divisible by n). So this produces the output:

1 | value1 | 1
2 | value2 | 1
3 | value3 | 1
4 | value4 | 2
5 | value5 | 2

If you just want the top or bottom half, you need to put this into a subquery, e.g.:

select theid, thevalue from (
  select theid, thevalue, ntile(2) over(order by theid) as tile_nr from thetable
) x
where x.tile_nr = 1

will return the top half, and similarly use x.tile_nr = 2 for the bottom half

Answer 3

You could use these two queries:

SELECT * FROM (
    SELECT *, ROW_NUMBER() OVER (ORDER BY TheID) AS rn FROM TheTable
) T1
WHERE rn % 2 = 0

SELECT * FROM (
    SELECT *, ROW_NUMBER() OVER (ORDER BY TheID) AS rn FROM TheTable
) T1
WHERE rn % 2 = 1

Answer 4

This is the query I found useful (after modifications of-course):

DECLARE @numberofitemsperpage INT DECLARE @numberofpages INT DECLARE @currentpage int

DECLARE @countRecords float SET @countRecords = (Select COUNT(*) From sz_hold_visitsData) -- the Excel can hold approximately ONE MILLION records at a time. if @countRecords >= 1000000 SET @numberofitemsperpage = 500000 ELSE IF @countRecords < 1000000 AND @countRecords >= 500000 SET @numberofitemsperpage = 250000 ELSE IF @countRecords < 500000 AND @countRecords >= 100000 SET @numberofitemsperpage = 50000 ELSE SET @numberofitemsperpage = 10000

DECLARE @numberofpages_deci float SET @numberofpages_deci = @countRecords / @numberofitemsperpage

SET @numberofpages = CEILING(@numberofpages_deci) Select @countRecords AS countRecords, @numberofitemsperpage AS numberofitemsperpage , @numberofpages_deci AS numberofpages_deci, @numberofpages AS numberofpagesFnl

SET @currentpage =0 WHILE @currentpage < @numberofpages BEGIN SELECT a.* FROM (SELECT row_number() OVER (ORDER BY person_ID) AS ROW, * FROM sz_hold_visitsData) a WHERE ROW >= @currentpage * @numberofitemsperpage +1 AND Row <= (@currentpage+1) * @numberofitemsperpage

IF @@ROWCOUNT = 0 BREAK SET @currentpage = @currentpage +1 END

In this extract, "sz_hold_visitsData" is a table in my database, whilst "person_ID" is a column therein. You can also further modify the script to output to file:

DECLARE @numberofitemsperpage INT DECLARE @numberofpages INT DECLARE @currentpage int

DECLARE @countRecords float SET @countRecords = (Select COUNT(*) From sz_hold_visitsData) -- the Excel can hold approximately ONE MILLION records at a time. if @countRecords >= 1000000 SET @numberofitemsperpage = 500000 ELSE IF @countRecords < 1000000 AND @countRecords >= 500000 SET @numberofitemsperpage = 250000 ELSE IF @countRecords < 500000 AND @countRecords >= 100000 SET @numberofitemsperpage = 50000 ELSE SET @numberofitemsperpage = 10000

DECLARE @numberofpages_deci float SET @numberofpages_deci = @countRecords / @numberofitemsperpage

SET @numberofpages = CEILING(@numberofpages_deci) Select @countRecords AS countRecords, @numberofitemsperpage AS numberofitemsperpage , @numberofpages_deci AS numberofpages_deci, @numberofpages AS numberofpagesFnl

DECLARE @sevrName nvarchar(50) SET @sevrName = '.\sql14' DECLARE @outputFile nvarchar(500)

SET @currentpage =0 WHILE @currentpage < @numberofpages BEGIN --SELECT a.* FROM (SELECT row_number() OVER (ORDER BY person_ID) AS ROW, * FROM sz_hold_visitsData) a WHERE ROW >= @currentpage * @numberofitemsperpage +1 AND Row <= (@currentpage+1) * @numberofitemsperpage SET @outputFile = 'C:\PSM\outVisits_' +convert(nvarchar(50), @currentpage) + '.csv' --Select @outputFile --TEST

DECLARE @cmd_ varchar(500) = 'sqlcmd -S ' + @sevrName + ' -E -Q "SELECT a.* FROM (SELECT row_number() OVER (ORDER BY person_ID) AS ROW, * FROM sz_hold_visitsData) a WHERE ROW >= '+ CONVERT(nvarchar(500),@currentpage * @numberofitemsperpage +1) +' AND Row <= ' + CONVERT(nvarchar(500),((@currentpage+1) * @numberofitemsperpage)) +'" -s "," -o ' +@outputFile +' ' -- "C:\PSM\outVisits.csv" ' EXEC xp_cmdshell @cmd_

IF @@ROWCOUNT = 0 BREAK SET @currentpage = @currentpage +1 END

Hope helps.

Answer 5

try this:

DECLARE @CountOf int,@Top int,@Bottom int
SELECT @CountOf=COUNT(*) FROM YourTable
SET @Top=@CountOf/2
SET @Bottom=@CountOf-@Top
SELECT TOP (@Top) * FROM YourTable ORDER BY 1 asc --assumes column 1 is your PK
SELECT TOP (@Bottom) * FROM YourTable ORDER BY 1 desc --assumes column 1 is your PK

Answer 6

Here is another solution:

You would need to use a temp table to hold the first 50% as below:

select top 50 percent * 
into #YourTempTable
from TheTable 

-- The below would give the first half
select * from #YourTempTable

-- The below woud give rest of the half 
select * from TheTable where TheID not in (select TheID from #YourTempTable)