TSQL Tutorials : Aggregate Columns

Aggregate columns consist of special functions that perform some calculation on a set of data. Examples

Of aggregates include the COUNT(), SUM(), AVG(), MIN(), STDDEV(), VAR(), and MAX() functions. They're

Best understood by example. Here's a command that returns the total number of customer records on file:

SELECT COUNT(*) FROM customers

Here's one that returns the dollar amount of the largest order on file:

SELECT MAX(Amount) FROM orders

And here's one that returns the total dollar amount of all orders:

SELECT SUM(Amount) FROM orders

Aggregate functions are often used in tandem with SELECT's GROUP BY clause (covered below) to produce

grouped or partitioned aggregates. They can be employed in other uses as well (e.g., to "hide" normally

invalid syntax), as the chapters on statistical computations illustrate.

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