GROUP BY CLAUSE

The GROUP BY clause is used to organize output rows into groups.

Group by clause can be used with different clauses. That are given below

Group by with where Group by with null Group by with all Group by with having

The where clause can be used with group by clause to restrict the row for grouping.

The rows that satisfy the search condition are considered fro grouping.

Example : Select cust_id ,sum(salary) from customer

where cust_name like ‘m%’ group by cust_id.

GROUP BY WITH WHERE

If the grouping column contain a null value, that row become a separate group in the result set.

Example: select student_class,count(student_class)

from student where student_class=‘null' group by student_class

GROUP BY WITH NULL

ALL is significant only when the SELECT has a WHERE clause. When ALL is used. It includes all the group by clause produces. It even includes those groups which do not meet the search conditions.

Example:

Select job,sum(salary) from emp where job like 's%' or job like 'c% 'group by all job

GROUP BY WITH ALL

Group by clause also uses operator like Cube Rollup Example:

SUMMARIZING DATA

Item Color quantity

Table Blue 124Table Red 223Chair Blue 101Chair Red 210

Generates the simple GROUP BY aggregate rows, plus subtotal or super-aggregate rows, and also a grand total row.

Example: Select

item_name,item_color,sum(item_quantity) from item group by item_name,item_color with rollup

Rollup

Output

CUBE is an aggregate operator that produces a super aggregate row.

Example: select

item_name,item_color,sum(item_quantity) as total from item group by item_name,item_color with cube

CUBE

Item Color Quantity_sumChair Blur 101Chair Red 210Chair Null 311Table Blue 124Table Red 223Table Null 347Null Null 658Null Blue 225null red 433

Output

CUBE generates a result set that shows

aggregates for all combinations of values in the selected columns.

ROLLUP generates a result set that shows aggregates for a hierarchy of values in the selected columns.

Differences between CUBE and ROLLUP: