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SQL Tutorial for Beginners

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SQL Count, Sum, Avg

Similar to the previous chapter, SUM, AVG, and COUNT functions are aggregate functions that return the sum of field, average value, and count. SUM and AVG can be applied only for numbers, and COUNT - for fields of any data type.

SELECT AVG(price) FROM songs

              
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SELECT AVG(price) FROM songs
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If you want to find the number of records with some condition, you can apply COUNT to the *.

This query outputs the number of records with the release date in the 20th century:

SELECT COUNT(*) FROM songs
WHERE year <= 2000

              
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SELECT COUNT(*) FROM songs
WHERE year <= 2000
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Aggregate functions and Distinct

If you want to apply aggregate function to the unique values, write DISTINCT inside this function and before the column name:

SELECT COUNT(DISTINCT song) FROM songs

              
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SELECT COUNT(DISTINCT song) FROM songs
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Tehtävä

Swipe to start coding

Now you have to write a query that helps you to calculate the total number of singers. Remember that some singers have two or more records in the table, but you have to pick these singers only once.

Ratkaisu

select count(distinct singer)
from songs

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