Query to select Single Best Record based on a Column Value

Question

Query to select Single Best Record for each NameID, grouped by Date, My DataTable under Zoho Reports.

----->

ID  Name ID Name    Others Colmns   Date n Time Error Count     Best Unique Record for the Date
1   W0026   Hari      x  ¦    x   ¦     2013,08,30 14:09:18 13      
2   W0027   Johnson   x  ¦    x   ¦     2013,08,30 14:01:44 0       < This Record for Date 30th
3   W0029   Prem      x  ¦    x   ¦     2013,08,30 14:04:04 2       
4   W0038   Philip    x  ¦    x   ¦     2013,08,30 14:00:20 0       < This Record for Date 30th
5   W0039   Amit      x  ¦    x   ¦     2013,08,30 14:08:03 6       <Can Select Eihter of record ID's( 5 and 10) as Error Count of both ID's is Same, for Date 30th 
6   W0026   Hari      x  ¦    x   ¦     2013,08,30 8:09:18  10      < This Record for Date 30th
7   W0027   Johnson   x  ¦    x   ¦     2013,08,30 8:01:44  4       
8   W0029   Prem      x  ¦    x   ¦     2013,08,30 8:04:04  0       < This Record for Date 30th
9   W0038   Philip    x  ¦    x   ¦     2013,08,30 8:00:20  1       
10  W0039   Amit      x  ¦    x   ¦     2013,08,30 8:08:03  6       
11  W0026   Hari      x  ¦    x   ¦     2013,08,29 14:09:18 5       < This Record for Date 29th
12  W0027   Johnson   x  ¦    x   ¦     2013,08,29 14:01:44 1       
13  W0029   Prem      x  ¦    x   ¦     2013,08,29 14:04:04 1       < Latest or Any one if Error Count is Same (between ID 5 and 10) for Date 29th
14  W0038   Philip    x  ¦    x   ¦     2013,08,29 14:00:20 0       < This Record for Date 29th
15  W0039   Amit      x  ¦    x   ¦     2013,08,29 14:08:03 6       
16  W0026   Hari      x  ¦    x   ¦     2013,08,29 8:09:18  8       
17  W0027   Johnson   x  ¦    x   ¦     2013,08,29 8:01:44  0       < This Record for Date 29th
18  W0029   Prem      x  ¦    x   ¦     2013,08,29 8:04:04  1       
19  W0038   Philip    x  ¦    x   ¦     2013,08,29 8:00:20  1       
20  W0039   Amit      x  ¦    x   ¦     2013,08,29 8:08:03  0       < This Record for Date 29th

-------> Where On each Working Date I get 2 Records for every Name ID. I need to Query out the Best record(Complete Row).

Best Record is selected based on the least value(Better Record) under column “Error Count” Grouped on Date and Result Sorted on Name ID . As shown in OutPut Table below.

xxxxx>>>> Output expected from Query

    ID  Name ID Name      x  ¦    x   ¦     Date & Time Error Count                 Comment
    6   W0026   Hari      x  ¦    x   ¦     2013,08,30 8:09:18  10      
    2   W0027   Johnson   x  ¦    x   ¦     2013,08,30 14:01:44 0       
    8   W0029   Prem      x  ¦    x   ¦     2013,08,30 8:04:04  0        < BEST in Each Name ID on 30th
    4   W0038   Philip    x  ¦    x   ¦     2013,08,30 14:00:20 0       
    5   W0039   Amit      x  ¦    x   ¦     2013,08,30 14:08:03 6       
    11  W0026   Hari      x  ¦    x   ¦     2013,08,29 14:09:18 5       
    17  W0027   Johnson   x  ¦    x   ¦     2013,08,29 8:01:44  0       
    13  W0029   Prem      x  ¦    x   ¦     2013,08,29 14:04:04 1        < BEST in Each Name ID on 29th
    14  W0038   Philip    x  ¦    x   ¦     2013,08,29 14:00:20 0       
    20  W0039   Amit    

  x  ¦    x   ¦     2013,08,29 8:08:03  0

xxxxxxx>>>

I am using the Zoho Reports(Entry Free Edition), Zoho Reports supports Simple SELECT SQL Querying in multiple dialects like ANSI, Oracle, Microsoft SQL Server, IBM DB2, MySQL, Sybase, PostgreSQL and Informix dialects. we can execute queries written in any of this dialects.

Below is my Query , I feel there is Better way to Query, Pls Suggest. (FYI: As of now zohoReports does not support SELECT query in FROM clause)

SELECT  myTable.* FROM "myTable"
 WHERE myTable."ID"= (SELECT T."ID"=myTable."ID"
   FROM "myTable" AS T
  WHERE T."Error Count" < myTable."Error Count"
ORDER BY myTable."Error Count" DESC
LIMIT 1) 
GROUP BY myTable."Name ID", DATE(myTable."Date n Time")

For Above Query I am getting Error as "Whenever a table alias is defined, kindly use table alias name before the respective columns used in SELECT query" But I have feel it is met. I am Struck here , need your Help.

Answer 1

I don't know anything about Zoho. However, the following idea should work in all the databases you mention:

SELECT myTable.*
FROM "myTable"
WHERE myTable."ID" = (SELECT T."ID"
                      FROM "myTable" T
                      WHERE cast(T."date n time" as date) < cast(myTable."date n time" as date) and
                            T.Name = myTable.Name
                      ORDER BY myTable."Error Count"
                      LIMIT 1
                     ) 

Two database differences are relevant. The first is the conversion from a datetime to a date. That might be database dependent. The second is limiting the results to one row. Different database have different ways of doing this.

This is using something called a correlated subquery. It fetches all rows that match on the date and name, and then returns the id from the row with the lowest error count.