109 lines
3.9 KiB
Markdown
109 lines
3.9 KiB
Markdown
---
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title: SQL COUNT Aggregate Function
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---
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## 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.
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This function will count the number of rows and return that count as a column in the result set.
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Here are examples of what you would use COUNT for:
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* Counting all rows in a table (no group by required)
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* Counting the totals of subsets of data (requires a Group By section of the statement)
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For reference, here is the current data for all the rows in our example student database.
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```sql
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select studentID, FullName, programOfStudy, sat_score from student; -- all records with fields of interest
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```
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Result :
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```text
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+-----------+------------------+----------------+-----------+
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| studentID | FullName | programOfStudy | sat_score |
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+-----------+------------------+----------------+-----------+
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| 1 | Monique Davis | Literature | 400 |
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| 2 | Teri Gutierrez | Programming | 800 |
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| 3 | Spencer Pautier | Programming | 1000 |
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| 4 | Louis Ramsey | Programming | 1200 |
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| 5 | Alvin Greene | Photography | 1400 |
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| 6 | Sophie Freeman | Photography | 1600 |
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| 7 | Maximo Smith | Photography | 1800 |
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| 8 | Michael Roach | Literature | 800 |
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+-----------+------------------+----------------+-----------+
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```
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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".
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```sql
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select count(*) AS studentCount from student; -- count of all records
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```
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Result :
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```text
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+--------------+
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| studentCount |
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+--------------+
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| 8 |
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+--------------+
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```
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* Here we get a count of students in each field of study.
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```sql
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select programOfStudy, count(*) AS studentCount from the student table with a group by programOfStudy;
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```
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Result :
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```text
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+----------------+--------------+
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| programOfStudy | studentCount |
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+----------------+--------------+
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| Literature | 2 |
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| photography | 3 |
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| programming | 3 |
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+----------------+--------------+
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```
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* Here we get a count of students with the same SAT scores.
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```sql
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select sat_score, count(*) AS studentCount from the student table with a group by sat_score;
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```
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Result :
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```text
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+-----------+--------------+
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| sat_score | studentCount |
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+-----------+--------------+
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| 400 | 1 |
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| 800 | 2 |
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| 1000 | 1 |
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| 1200 | 1 |
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| 1400 | 1 |
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| 1600 | 1 |
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| 1800 | 1 |
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+-----------+--------------+
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```
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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.
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```sql
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select Specific_Party, Election_Year, format(sum(Total_$),2) AS contribution$Total, count(*) AS numberOfContributions
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from combined_party_data
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group by Specific_Party,Election_Year
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having Election_Year = 2016;
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```
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Result :
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```text
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+----------------+---------------+--------------------+-----------------------+
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| Specific_Party | Election_Year | contribution$Total | numberOfContributions |
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+----------------+---------------+--------------------+-----------------------+
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| DEMOCRATIC | 2016 | 833,592,846.09 | 361 |
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| REPUBLICAN | 2016 | 676,149,662.07 | 1247 |
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+----------------+---------------+--------------------+-----------------------+
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```
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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.
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