Difference between COUNT(*) vs COUNT(column).

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ICSM Computer · Answer

In SQL, both COUNT(*) and COUNT(column) count rows, but they behave differently with NULL values. COUNT(*) Counts all rows in the result set, including rows where columns contain NULL. Example: If the table has 10 rows, result = 10. COUNT(column) Counts only rows where the specified column is NOT NULL. Example: If email has: id email 1 a@example.com 2 NULL 3 b@example.com Then: Key Difference Function Counts NULLs? What it counts COUNT(*) Yes All rows COUNT(column) No Non-NULL values in that column With GROUP BY Example: COUNT(*) → total employees in each departmentCOUNT(manager_id) → employees whose manager_id is not NULL Performance Notes In modern databases (like PostgreSQL, MySQL, SQL Server, Oracle): COUNT(*) is usually optimized and preferred for counting rows.COUNT(1) and COUNT(*) are generally equivalent in performance.COUNT(column) may behave differently because it must check for NULLs. Quick Rule Use: COUNT(*) → when you want total row countCOUNT(column) → when you want count of non-null values in a specific column

Difference between COUNT(*) vs COUNT(column).

1 Answers

`COUNT(*)`

`COUNT(column)`

Key Difference

With `GROUP BY`

Performance Notes

Quick Rule

Function	Counts NULLs?	What it counts
`COUNT(*)`	Yes	All rows
`COUNT(column)`	No	Non-NULL values in that column

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Difference between COUNT(*) vs COUNT(column).

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1 Answers

COUNT(*)

COUNT(column)

Key Difference

With GROUP BY

Performance Notes

Quick Rule

`COUNT(*)`

`COUNT(column)`

With `GROUP BY`