3. SUM(expr)
SUM(DISTINCT expr) provides a total by adding all the unique values returned
after expr is evaluated for each row in the group. SUM(expr) and SUM(ALL expr)
provide a total by adding expr for each row in the group. Null values are ignored.
The expr parameter must be a numeric value. Consider the following queries:
Query 1: select sum(2) from employees;
Query 2: select sum(salary) from employees;
P AR T II
Query 3: select sum(distinct salary) from employees;
Query 4: select sum(commission_pct) from employees;
There are 107 rows in the EMPLOYEES table. Query 1 adds the number 2 across
107 rows and returns 214. Query 2 takes the SALARY column value for every row in
the group, which in this case is the entire table, and returns the total salary amount of
Bạn đang xem 3. - OCA OCP ORACLE DATABASE 11G A LL IN ONE EXAM GUIDE P51 PPS
