Paging in SQL with no break on primary key - sql

Question

I am new to Stackoverflow. Please forgive me if I have made some mistake.
I have following data in SQL.
Row No. Customer No. Customer Name
------------------------------------------------------------
1 1234 ABCD
2 1234 ABCD
3 1234 ABCD
4 6789 WXYZ
5 6789 WXYZ
6 3456 OPQR
7 4567 JKLM
I need to page the above data with following constraint
Page size : 4 records
If customer no. is splitting between two pages then new customer no. should go on the next page.
output desired:
Paging with 4 records each page
1st Page
Row No. Customer No. Customer Name
------------------------------------------------------------
1 1234 ABCD
2 1234 ABCD
3 1234 ABCD
2nd Page
Row No. Customer No. Customer Name
------------------------------------------------------------
4 6789 WXYZ
5 6789 WXYZ
6 3456 OPQR
7 4567 JKLM
Please help.

Answer 1

You can read page size +1 records using any limiting, then if the last record and the record before the last has the same Customer Name just filter out the customer using HAVING.
Could be tricky and depends on DB you use and could be easily done on presentation layer

Answer 2

Declare #PageNumber INT = 1, #PageSize INT = 4
;with cte1(RowNo,CustomerNo,CustomerName)
AS
(
Select 1,1234,'ABCD' union all
Select 2,1234,'ABCD' union all
Select 3,1234,'ABCD' union all
Select 4,6789,'WXYZ' union all
Select 5,6789,'WXYZ' union all
Select 6,3456,'OPQR' union all
Select 7,4567,'JKLM'
)
select * from cte1 order by RowNo
OFFSET #PageSize * (#PageNumber - 1) ROWS
FETCH NEXT #PageSize ROWS ONLY

Answer 3

This can be done and not to complicated using recursive CTE.
For sample data, I have used query from other answer
WITH cte1(RowNo,CustomerNo,CustomerName)
AS
(
SELECT 1,1234,'ABCD' UNION ALL
SELECT 2,1234,'ABCD' UNION ALL
SELECT 3,1234,'ABCD' UNION ALL
SELECT 4,6789,'WXYZ' UNION ALL
SELECT 5,6789,'WXYZ' UNION ALL
SELECT 6,3456,'OPQR' UNION ALL
SELECT 7,4567,'JKLM'
)
SELECT * INTO #table FROM cte1
I'l add one more row with reapaing user to split this to 3rd page
INSERT #table (RowNo, CustomerNo, CustomerName) VALUES (8,3456,'OPQR')
And here is the solution. I've put some comments to explain parts
WITH CTE_Source AS
(
--I use this to add RN column simply beacuse I can't trust that rowNo column will have no gaps
SELECT *
, ROW_NUMBER() OVER (ORDER BY RowNo) RN
FROM #table t
)
, CTE_R AS
(
--First part is select of first row
SELECT s.RowNo
, s.CustomerNo
, s.CustomerName
, s.RN
, 1 AS Grp --this is a current group of rows
, 1 AS Cnt --counter of how many rows group have
FROM CTE_Source s WHERE RN = 1
UNION ALL
--subsequent select is for next row
SELECT
s.RowNo
, s.CustomerNo
, s.CustomerName
, s.RN
-- increase group when different customer
, CASE WHEN s.CustomerNo = r.CustomerNo THEN r.Grp ELSE r.Grp+Cnt END
-- increase counter when same customer
, CASE WHEN s.CustomerNo = r.CustomerNo THEN r.Cnt + 1 ELSE 1 END
FROM CTE_R r
INNER JOIN CTE_Source s ON s.RN = r.Rn + 1
)
, CTE_Paging AS
(
SELECT *
, CEILING((r.Grp + r.Cnt) / 4.) AS Page -- replace 4 with your page size
FROM CTE_R r
)
SELECT * FROM CTE_Paging --Just add WHERE Page = if you want specific page
OPTION (MAXRECURSION 0) -- for unlimited recursion if you have more than 100 rows