Month: October 2017

MS SQL Azure – SQL to Select Distinct list of Child Records based on a Maximum or Minimum Child Field Value

Following on from the previous post I wanted to know the syntax for SQL to do the same but in SQL Azure. 

SELECT * FROM dbo.T02AttendanceGame T1    
WHERE Attendance = (
   SELECT max(Attendance)
   FROM dbo.T02AttendanceGame T2
   WHERE T1.FKID=T2.FKID
);

I created the same tables that I created for the MS Access example with the same field names but within a SQL Azure database.

Here’s the same SQL but then creating a view called rather unimaginatively ‘View01’

CREATE VIEW VIEW01 AS SELECT * FROM dbo.T02AttendanceGame T1    
WHERE Attendance = (
   SELECT max(Attendance)
   FROM dbo.T02AttendanceGame T2
   WHERE T1.FKID=T2.FKID
);

MS Access – SQL to Select Distinct list of Child Records based on a Maximum or Minimum Child Field Value

So we have a table of Stadiums and a table of attendances. We would like to create a query that shows an individual child record for each stadium of the highest attendances. Quite often you seek the latest or earliest child record by grouping on the primary key of the child record but what happens if you needing to identify a child not on the latest or earliest but on a value that does not correlate with the order in which the records have been created. In such a case the primary key can no longer act as a proxy for minimum or maximum value of the required field.

To demonstrate the problem and to illustrate it I create two tables

T01Stadium with the fields
PKID
Location

and

T02AttendanceGame with the fields
PKID
FKID
Attendance
GameDate
Date
Weather

and these are the example values I entered.

and here’s the code that shows the maximum attendance in the child records

SELECT *
FROM T02AttendanceGame AS G1 INNER JOIN [SELECT FKID, MAX(Attendance) AS HAttend FROM T02AttendanceGame GROUP BY FKID]. AS G2 ON (G1.Attendance=G2.HAttend) AND (G1.FKID=G2.FKID)
ORDER BY G1.FKID;

and here’s similar code that shows the latest games played at the two stadia

SELECT *
FROM T02AttendanceGame AS G1 INNER JOIN [SELECT FKID, MAX(GameDate) AS LatestDate FROM T02AttendanceGame GROUP BY FKID]. AS G2 ON (G1.GameDate=G2.LatestDate) AND (G1.FKID=G2.FKID)
ORDER BY G1.FKID;

This is yet another very valuable structure with which to reduce the complexity of data for users who are quickly seeking to find key values in a child table when that data is coming in out of synch with the order of data entry. Individuals wishing to use this code will need to enter the MS Access SQL editor and will need to be careful as the graphics designer cannot represent this syntax. I have tested this code with MS Access 2003 as the front end and SQL Azure as the backend and I can confirm that it does work. I have not extensively tested it.