Aggregate Functions

Today, we will learn commonly used aggregate functions which are very handy for aggregation and statistical analysis.

COUNT()

The function returns the number of rows that matches a specific condition of a query.

There are different ways to use the function.

COUNT(*)

function returns the number of rows in the table, including NULL and duplicate rows.

Bear in mind that using the function on a large data set slows down the query because SQL must scan all the rows for all columns.

Example

COUNT(column)

The function returns the number of rows in the specific column. However, it does not consider NULL values in the column.

Example

COUNT(DISTINCT column)

The function returns the number of unique non-null values in the column.

Example

COUNT() with multiple columns

Example

COUNT() with condition

Example

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SUM()

returns the sum of values or distinct values. However, It ignores NULL values.

Example

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AVG()

function calculate the average value of a column.

Example

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MIN(), MAX()

The function returns the minimum value of a column and the function returns the maximum value of a column.

Example