MySQL SQLLesson 20Free preview

MySQL COUNT()

This lesson is part of MySQL · All levels

Summary

The COUNT() function calculates the number of rows that meet the criteria in your query. COUNT(*) counts all rows including those with columns NULL, whereas COUNT(column) only counts rows whose columns are not NULL. There is also COUNT(DISTINCT column) to calculate the number of unique values without duplicates.

Key points

Count the whole row regardless
COUNT(column) counts only rows with no NULL value on the column
Calculate the number of unique values
Often used together with GROUP BY to count per group

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