| 12. 1. 1. Using Aggregate Functions |
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Aggregate functions operate on a group of rows at the same time. |
Aggregate functions return one row of output for each group of rows. |
For example, computing the average salary of employees and finding the maximum salary of employees. |
Aggregate functions are also called group functions because they operate on groups of rows. |
The aggregate functions are mainly numerical. |
| Function | Description | | AVG(x) | Returns the average value of x. | | COUNT(x) | Returns the number of rows returned by a query involving x. | | GLC | Greatest lower bound of an MLSLABEL. | | LUB | Least upper bound of an MLSLABEL. | | MAX(x) | Returns the maximum value of x. | | MEDIAN(x) | Returns the median value of x. | | MIN(x) | Returns the minimum value of x. | | STDDEV(x) | Returns the standard deviation of x. | | SUM(x) | Returns the sum of x. | | VARIANCE(x) | Returns the variance of x. |
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Here are some points to remember when using aggregate functions |
- COUNT(), MAX(), and MIN() functions operate numbers, strings, and datetimes.
- Null values are ignored by aggregate functions.
- DISTINCT keyword with an aggregate function excludes duplicate entries from the aggregate function's calculation.
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