SQL Aggregate Functions

Since we have started dealing with numbers, the next natural question to ask is if it is possible to do math on those numbers, such as summing them up or taking their average. The answer is yes! SQL has several arithematic functions, and they are:

- AVG
- COUNT
- MAX
- MIN
- SUM

The syntax for using functions is,

SELECT "function type"("column_name")
FROM "table_name"

For example, if we want to get the sum of all sales from the following table,

Table Store_Information

store_name	Sales	Date
Los Angeles	$1500	Jan-05-1999
San Diego	$250	Jan-07-1999
Los Angeles	$300	Jan-08-1999
Boston	$700	Jan-08-1999

we would type in

SELECT SUM(Sales) FROM Store_Information

Result:

$2750 represents the sum of all Sales entries: $1500 + $250 + $300 + $700.

In addition to using functions, it is also possible to use SQL to perform simple tasks such as addition (+) and subtraction (-). For character-type data, there are also several string functions available, such as concatenation, trim, and substring functions. Different RDBMS vendors have different string functions implementations, and it is best to consult the references for your RDBMS to see how these functions are used.