Query Tutorials Index:
|Select Sum||Total (count) of the field values|
|Select Avg||Average of the field values|
|Select Min||Lowest (minimum) field value|
|Select Max||Highest (maximum) field value|
|Select Count||Count of the values other than nulls|
|Select StDev||Standard deviation of the field values including date/time fields|
|Select Var||Variance of the field values including date/time|
Here are some examples of aggregate function usage:
Select Count Aggregate Function Query
Select Count(Emp_ID) From M_Employees;
The query above simply counts the autonumber field in the M_Employees table.
Select Average Aggregate Function Example
Select Avg(Emp_Salary) From M_Employees Where Emp_Age<50;
The above aggregate query determines the average salary for employees under 50 years of age.
The SQL aggregate query below gets a little interesting by showing you how to answer more complex question of your data:
SELECT avg(iif(emp_age>=50,Emp_Salary,null)) as Over_50_Salary,avg(iif(emp_age<50,emp_salary,null)) as
Note the use of the immediate if (iif) to bracket the results and return two columns where the would normally be only one.
Note there is no Group By which is normally associated with an SQL aggregate function query.
Note we are using aliases (as) to generate our own column names.
Note nulls are skipped in the average aggregate and that is what makes this query work.
Select StDev Query
Using the Employee table shown above now we get the standard deviation of the salary column:
SELECT StDev([Emp_Salary]) AS Salary_Standard_Deviation FROM M_Employees;
Results are pretty simple:
SQL Select Var Aggregate Variance Query
SELECT Var([Emp_Salary]) AS Salary_Variance FROM M_Employees;
The results are shown below:
Here are some additional techniques to consider...
When creating a report it is often useful to have the Count Average and Standard Deviation listed at the bottom of each column of numbers. As fairly simple technique is to use a series of union queries to build the result rows.
The first query would retrieve all the raw numbers in a multi row list.
The second union query would append the aggregate count function.
The third union query would add the aggregate average function. Finally the last union select would add the standard deviation.
Another technique to try out is to use the aggregate functions in the scalar query.
More Aggregate Function Information:
Domain Aggregate Functions in MS Access
SQL Aggregate Function Examples: Dlookup, Dmin, Dmax, Dlast, Dfirst, DAvg, DSum, Dcount, DStdev, DstdevP,Dvar, DvarP...
Advanced Union Query Download
In this example we selecting the individual data records from the table and at the same time using the union query function to select SQL Aggregate functions...
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