Sql-server – Select fixed number of records/rows from growing table from SQL Server

querysql server

Background: A SQL-Server database table is used to store weekly reports of some system memory usage, meaning that each week a new table row/record/line is inserted.

The question is how a fixed number (e.g. 5 records) of records can be queried, with the side-condition that those records are equally spaced within the time-range.

if this was the table

id | memory
----------- 
01  1231
02  1241
03  1260
04  1300
[.... other 92 rows ...]
97  2001
98  2002
99  2020

and with said 5 records I would like have a table as such

id | memory
----------- 
01  1231
25  1600
50  1800
75  1900
99  2020

since it would most represent the overall picture of the data.

Best Answer

There's probably a more elegant way to achieve this but it can be done by using the NTILE function inside a CTE.

WITH cte AS (

  SELECT NTILE(5) OVER (ORDER BY id asc) AS dist,
  memory
  FROM TABLE)

  SELECT TOP 1 id, memory FROM cte WHERE dist = 1

  UNION

   SELECT TOP 1 id, memory FROM cte WHERE dist = 2

  UNION

   SELECT TOP 1 id, memory FROM cte WHERE dist = 3

  UNION

   SELECT TOP 1 id, memory FROM cte WHERE dist = 4

  UNION

   SELECT TOP 1 id, memory FROM cte WHERE dist = 5;

Related Solutions

Sql-server – T-sql: Select most specific match from table

My first step would be to rank the service_instruction by specificity/generality - I don't think you have provided enough information to be sure what you are after but assuming that it is based on the number of 1s and ties are broken by: bank_num is more specific than loan_type_cd is more specific than client_num:

select *, row_number() over ( order by case when bank_num=1 then 1 else 0 end+
                                       case when loan_type_cd=1 then 1 else 0 end+
                                       case when client_num=1 then 1 else 0 end,
                                     case when bank_num=1 then 1 else 0 end,
                                     case when loan_type_cd=1 then 1 else 0 end,
                                     case when client_num=1 then 1 else 0 end ) as gen
from service_instruction;

produces:

instruction_num service_num instruction_desc    bank_num    region_num  loan_type_cd    client_num  gen
3   251 Take the photos, yeah   17  96  3   1   1
4   251 Bid for debris removal. 1   471 1   7   2
7   251 Bid for debris removal. Do not perform  1   3   1   1   3

This can then be joined to order and work_order_line and filtered for the row for each work_order_line_num with the lowest generality (gen), perhaps something like this:

with w as (
    select *, row_number() over ( order by case when bank_num=1 then 1 else 0 end+
                                           case when loan_type_cd=1 then 1 else 0 end+
                                           case when client_num=1 then 1 else 0 end,
                                         case when bank_num=1 then 1 else 0 end,
                                         case when loan_type_cd=1 then 1 else 0 end,
                                         case when client_num=1 then 1 else 0 end ) as gen
    from service_instruction )
select *
from( select l.*, instruction_desc, row_number() over ( partition by l.work_order_line_num, 
                                                                     l.order_num, 
                                                                     l.service_num
                                                        order by gen ) as gen_rank
      from work_order_line l join [order] o on(o.order_num=l.order_num)
           join w on( l.service_num=w.service_num 
                      and (o.bank_num=w.bank_num or w.bank_num=1) 
                      and (o.loan_type_cd=w.loan_type_cd or w.loan_type_cd=1)
                      and (o.client_num=w.client_num or w.client_num=1)) ) z
where gen_rank=1

which produces:

work_order_line_num order_num   service_num instruction_desc    gen_rank
20  1   251 Bid for debris removal. Do not perform  1
21  2   251 Bid for debris removal. 1
22  3   251 Take the photos, yeah   1
26  4   251 Bid for debris removal. Do not perform  1

notes:

I've assumed you need to partition by work_order_line_num, order_num and service_num but maybe not all are necessary depending on the PK of work_order_line
I've ignored the pricing_region complexity you mention but don't specify completely - hopefully you'll be able to work it into the query in a similar manner to the rest
You'll probably have to fix the CTE with your rules for specificity/generality
I tested on 2008R2 - YMMV if you are on an earlier version

Sql-server – SQL Server select records from header and body table

I don't see why this won't work:

IF OBJECT_ID(N'dbo.Header', N'U') IS NOT NULL
DROP TABLE dbo.Header;
IF OBJECT_ID(N'dbo.Body', N'U') IS NOT NULL
DROP TABLE dbo.Body;
GO
CREATE TABLE dbo.Header
(
    iGroup int
    , sName varchar(50)
    , iValue int
);
CREATE TABLE Body
(
    iGroup int
    , sName varchar(50)
    , iValue int
);

INSERT INTO dbo.Header (iGroup, sName, iValue)
VALUES (1, 'test1', 10)
    , (2, 'test2', 20);

INSERT INTO dbo.Body (iGroup, sName, iValue)
VALUES (1, 'test3', 30)
    , (2, 'test4', 40);


;WITH src AS 
(
    SELECT iGroup
        , sName
        , iValue
        , 0 as sort_by
    FROM Header
    UNION ALL 
    SELECT iGroup
        , sName
        , iValue
        , 1 as sort_by
    FROM Body
)
SELECT Id = ROW_NUMBER() OVER (ORDER BY sort_by, iGroup, sName)
    , src.*
FROM src
ORDER BY sort_by, iGroup, sName;

Results:

╔════╦════════╦═══════╦════════╗
║ Id ║ iGroup ║ sName ║ iValue ║
╠════╬════════╬═══════╬════════╣
║  1 ║      1 ║ test1 ║     10 ║
║  2 ║      1 ║ test3 ║     30 ║
║  3 ║      2 ║ test2 ║     20 ║
║  4 ║      2 ║ test4 ║     40 ║
╚════╩════════╩═══════╩════════╝

Also, don't use reserved keywords as column names, please!

Best Answer

Related Solutions

Sql-server – T-sql: Select most specific match from table

Sql-server – SQL Server select records from header and body table

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