GROUP FUNCTION

Group functions operate on group of rows and return one value for the ENTIRE GROUP. As a group is consdered the entire table or just some portions of the table grouped by some common atribute.

Group functions are:

COUNT, MAX, MIN, AVG, SUM, DISTINCT

COUNT - It returns the number of rows in the query. For example: we want to know number of employees wich have salary = 10000



What will happen if in the group are rows with NULL values? They will not be considered!!!

For example: We have in the entire table 107 rows, but only 35 from them are with non-null values in collumn commission_pct





DISTINCT - we can use it to retrieve only unique data entries.

Example:



There will be selected just 57 rows. (all duplicate values will be ignored)

AVG - it returns the average value of the column or expression. For example:





As we can see from the examples, the general syntax from the AVG functions is:

AVG([DISTINCT] EXPRESSION)

MAX Function - it will return the highest number (when operation on numeric values), latest date (when operating on date) and the world that appears at last alphabetically ( when operating on char data.

Examples:





MIN Function - it is exactly the opposite of the MAX function. For example:





SUM Function -it returns the sum of values of expression. For more information, pls check ORACLE DOCUMENTATION Examples:

More functions are available under http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/functions163.htm