COUNT(*) vs. COUNT(column-name): Which SQL Aggregate Function Should I Use?

Which is More Correct: COUNT(*) vs. COUNT(column-name)?

The SQL aggregate function COUNT can be used in two ways: COUNT(*) and COUNT(column-name). While both methods aim to tally the number of rows, there are subtle differences to consider.

COUNT(*)

• Counts all rows, even those with NULL values.
• Useful when obtaining a total count of records without regard to data availability.

COUNT(column-name)

• Counts non-NULL values only.
• More specific and can be used to count the number of rows with a particular value or to filter out NULLs.

In your example code:

• COUNT(*): Counts all rows in the group, including any with missing values.
• COUNT(customerid): Counts only rows with customer IDs. It filters out any rows with NULL customer IDs.

Choosing between COUNT(*) and COUNT(column-name) depends on the desired output:

• To count the total number of rows, regardless of NULLs, use COUNT(*).
• To count non-NULL values only, use COUNT(column-name).

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