A commonly used aggregate function in SQL is COUNT(). COUNT() returns the number of rows that match the given criteria.

COUNT(*)

If we only want to see how many records are in a table (but not actually view those records), we could use COUNT(*). COUNT(*) returns everything — including null values and duplicates.

SQL statement

SELECT COUNT(*) FROM Individual;

Source Table

IndividualIdFirstNameLastNameUserName1FredFlinstonefreddo2HomerSimpsonhomey3HomerBrownnotsofamous4OzzyOzzbournesabbath5HomerGainnoplacelike6Bono
u2

Result

6

COUNT(column name)

If we want to see how many non-null values are in a given column, we use COUNT(column name) where column name is the name of the column we want to test.

SQL statement

SELECT COUNT(LastName) FROM Individual;

Source Table

IdFirstNameLastNameUserName1FredFlinstonefreddo2HomerSimpsonhomey3HomerBrownnotsofamous4OzzyOzzbournesabbath5HomerGainnoplacelike6Bono
u2

Result

5

Combining COUNT & DISTINCT

If we only want to see how many unique names are in the table, we could nest the DISTINCT inside a COUNT function.

SQL statement

SELECT COUNT(DISTINCT(FirstName)) FROM Individual;

Result

4