SQL COUNT Aggregate Function

SQL COUNT Aggregate Function
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The COUNT operator is usually used in combination with a GROUP BY clause. It is one of the SQL “aggregate” functions, which include AVG (average) and SUM.

This function will count the number of rows and return that count as a column in the result set.

Here are examples of what you would use COUNT for:

  • Counting all rows in a table (no group by required)
  • Counting the totals of subsets of data (requires a Group By section of the statement)

For reference, here is the current data for all the rows in our example student database.

select studentID, FullName, programOfStudy, sat_score from student; -- all records with fields of interest

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This SQL statement provides a count of all rows. Note that you can give the resulting COUNT column a name using “AS”.

select count(*) AS studentCount from student; -- count of all records

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Here we get a count of students in each field of study.

 select studentID, FullName, count(*) AS studentCount from the student table with a group by programOfStudy;

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Here we get a count of students with the same SAT scores.

 select studentID, FullName, count(*) AS studentCount from the student table with a group by sat_score;

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Here is an example using the campaign funds table. This is a sum total of the dollars in each transaction and the number of contributions for each political party during the 2016 US Presidential Campaign.

select Specific_Party, Election_Year, format(sum(Total_$),2) AS contribution$Total, count(*) AS numberOfContributions 
from combined_party_data
group by Specific_Party,Election_Year
having Election_Year = 2016;

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As with all of these things there is much more to it, so please see the manual for your database manager and have fun trying different tests yourself.