「 Aggregate Functions 」 List

COUNT function is used to count a number of rows. If you want to count only unique elements, you can use DISTINCT to exclude duplicated elements. Example 1: count a number of employees SELECT COUNT(*) FROM tbEmpTable; COUNT(*) 24 Example 2: count numbers of employees by each department. SELECT deptCD, COUNT(*) FROM tbEmpTable GROUP BY deptCD; deptCD COUNT(*) 100 3 200 10 300 7 400 4 Example 3: count a number of departments SELECT COUNT(DISTINCT deptCD) FROM tbEmpTable; COUNT(DISTINCT deptCD) 4

AVG function is used to calculate an average value from a selected field. Example1: Calculate an average value of employees’ salary. SELECT AVG(salary) FROM tbSalaryTable; AVG(salary) 254000 Example2: Calculate an average value of salary by each department. SELECT deptCD, AVG(salary) FROM tbSalaryTable GROUP BY deptCD; deptCD AVG(salary) 100 150000 200 203090 300 403200 400 305420