aggregate

AVG()

Calculates the average (mean) of the values in a numeric column across a group of rows.

Description

AVG is an aggregate function that computes the arithmetic mean of a numeric column: the sum of all the values divided by how many there are. It's commonly used for things like average test scores, average price, or average order size.

Syntax

AVG(column_name)

Parameters

Name	Description	Optional
expression	The numeric column or expression to average. NULL values are excluded from both the sum and the count used in the calculation.	No

Return Type

AVG returns a DOUBLE, since an average of integers is often not a whole number.

Examples

School (Students/Courses/Grades)

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School (Students/Courses/Grades)

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AVG ignores NULLs, it doesn't treat them as zero

If some rows have a NULL score, AVG(score) divides by the number of non-NULL scores, not the total row count. If you actually want NULLs treated as zero, wrap the column in COALESCE(score, 0) first.

Common Mistakes

Expecting a NULL score to count as zero. AVG silently skips NULLs, which can make an average look higher than expected if missing scores should really count as 0.
Not rounding the result. AVG often returns a long decimal like 86.33333333, which is worth wrapping in ROUND() for readability.
Averaging an already-averaged column. Taking AVG of a column that's itself a per-group average (instead of the raw values) gives a mathematically different, often incorrect, result.