Control break statements are statements which are used to control the sequence of execution of statements with in loop.....endloop.
These statements are executed only with in loop...endloop.
Control break statements are
AT FIRST - This statement is executed/triggered for the first iteration of loop (SY-TABIX = 1 ).
AT LAST - This statement is executed/triggered for the last iteration of loop.
AT NEW <FIELD> - This is executed whenever there is a new value on specified field.
AT END OF - This statement is executed whenever the new value ends on specific field.
ON CHANGE OF <FIELD> - It is same as AT NEW and is obsolete in ECC 6.0.