SUM function returns the summation of selected column. You can also obtain the sum excluding duplicate data using DISTINCT parameter, however, you rarely use DISTINCT parameter with SUM. example: Return the summation of employees’ age. SELECT SUM(age) FROM tbEmpTable; SUM(age) ————————– 123 example: Return the summation of employees’ age after excluding duplicate ages. SELECT SUM(DISTINCT [...]

STDDEV or STDEV function return the standard deviation of selected column. Standard deviation tells how much dispersion there is from an average value. Small standard deviation tells the each value is close to the average value. Large standard deviation indicates that the each value is spread out from average value. example: Return the standard deviation [...]

MIN function returns the minimum value of selected column. The value can be number, character, or datetime. example: Return the smallest salary of employees. SELECT MIN(salary) FROM tbEmpTable; MIN(salary) ————————— 120000 example: Return the smallest salary in each department. SELECT deptCD, MIN(salary) FROM tbEmpTable GROUP BY deptCD; deptCD, MIN(salary) —————————- 100 120000 200 156000 300 [...]

You can use MAX function to return the largest value of your selected column. The value can be number, character, datetime. example: Return the highest salary of employees. SELECT MAX(salary) FROM tbEmpTable MAX(salary) ——————————– 543000 example: Return the highest salary in each department. SELECT deptCD, MAX(salary) FROM tbEmpTable GROUP BY deptCD; deptCD, MAX(salary) ——————————– 100 [...]

COUNT function can count the number of records(rows). If you use DISTINCT, you can eliminate duplicated data and count the number of rows. example: to count the number of employees. SELECT COUNT(*) FROM tbEmpTable; COUNT(*) ———————- 24 example: count the number of employees in each department. SELECT deptCD, COUNT(*) FROM tbEmpTable GROUP BY deptCD; deptCD, [...]

AVG function returns average number from a specific column. example: to find average value of employees’ salary. SELECT AVG(salary) FROM tbSalaryTable; AVG(salary) —————————————– 254000