Aggregate functions return a single value for a set of rows. If there is no GROUP BY clause, an aggregate function returns a single value for all the rows that satisfy other aspects of the query.
List the number of employees in the company
In Interactive SQL, execute the following query:
SELECT COUNT( * ) FROM Employees; |
| COUNT(*) |
|---|
| 75 |
The result set consists of only one column, with title COUNT(*), and one row, which contains the total number of employees.
List the number of employees in the company and the birth dates of the oldest and youngest employee
In Interactive SQL, execute the following query:
SELECT COUNT( * ), MIN( BirthDate ), MAX( BirthDate ) FROM Employees; |
| COUNT(*) | MIN(Employees.BirthDate) | MAX(Employees.BirthDate) |
|---|---|---|
| 75 | 1936-01-02 | 1973-01-18 |
The functions COUNT, MIN, and MAX are called aggregate functions. Aggregate functions summarize information. Other aggregate functions include statistical functions such as AVG, STDDEV, and VARIANCE. All but COUNT require a parameter. See Aggregate functions.
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