Functions in Sql

Functions in SQL
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: Average of the column.
• COUNT: Number of records.
• MAX: Maximum of the column.
• MIN: Minimum of the column.
• SUM: Sum of the column.
The syntax for using functions is,
SELECT "function type" ("column_name")
FROM "table_name"
Examples of how these functions are used are presented individually in the next few pages.
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.

Aggregate Functions:

SQL uses the AVG() function to calculate the average of a column. The syntax for using this function is,

SELECT AVG("column_name")
FROM "table_name"

For example, if we want to get the average 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 AVG(Sales) FROM Store_Information

Result:

AVG(Sales)

$687.5

$687.5 represents the average of all Sales entries: ($1500 + $250 + $300 + $700) / 4.

Count Function:

Another arithmetic function is COUNT. This allows us to COUNT up the number of row in a certain table. The syntax is,

SELECT COUNT("column_name")
FROM "table_name"

For example, if we want to find the number of store entries in our 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'd key in

SELECT COUNT(store_name)
FROM Store_Information

Result:

Count(store_name)

4

COUNT and DISTINCT can be used together in a statement to fetch the number of distinct entries in a table. For example, if we want to find out the number of distinct stores, we'd type,

SELECT COUNT(DISTINCT store_name)
FROM Store_Information

Result:

Count(DISTINCT store_name)

3

Max Function:

SQL uses the MAX function to find the maximum value in a column. The syntax for using the MAX function is,

SELECT MAX("column_name")
FROM "table_name"

For example, if we want to get the highest 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 MAX(Sales) FROM Store_Information

Result:

MAX(Sales)

$1500

$1500 represents the maximum value of all Sales entries: $1500, $250, $300, and $700.

Min Function:

SQL uses the MIN function to find the maximum value in a column. The syntax for using the MIN function is,

SELECT MIN("column_name")
FROM "table_name"

For example, if we want to get the lowest 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 MIN(Sales) FROM Store_Information

Result:

MIN(Sales)

$250

$250 represents the minimum value of all Sales entries: $1500, $250, $300, and $700.

Sum Function:

The SUM function is used to calculate the total for a column. The syntax is,

SELECT SUM("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:

SUM(Sales)

$2750

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