MySql
Aggregate Function
AVG(expr)
Returns the average value of expr. AVG() returns NULL if there were no matching rows.
example 1 :
SELECT student_name, AVG(test_score) FROM student // returns average test_score.
COUNT(expr)
Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement. The result is a BIGINT value. COUNT() returns 0 if there were no matching rows.
example 1 :
SELECT COUNT(gen) FROM gender ;// 2 COUNT(*) is somewhat different in that it returns a count of the number of rows retrieved, whether or not they contain NULL values.
example 2 :
SELECT COUNT(*) FROM gender; // 3
SUM(expr)
Returns the sum of expr. SUM() returns NULL if there were no matching rows.
example 1 :
SELECT SUM(salary) AS gp_total_sal FROM emp GROUP BY team HAVING team_size <5; // Returns the sum of the salary of every group having team size less than 5.
MAX([DISTINCT] expr)
Returns the maximum value of expr. MAX() returns NULL if there were no matching rows.
example 1 :
SELECT MAX(test_score) FROM student GROUP BY student_name; //Returns the maximum test_score of individual student.
MIN([DISTINCT] expr)
Returns the minimum value of expr. MIN() returns NULL if there were no matching rows.
example 1 :
SELECT MIN(test_score), MAX(test_score) FROM student GROUP BY student_name; //Returns the minimum and maximum test_score of individual student.
GROUP_CONCAT(expr)
This function returns a comma separated string result with the concatenated non-NULL values from a group. It returns NULL if there are no non-NULL values.
example 1 :
SELECT GROUP_CONCAT(test_score) AS cm_separated FROM student GROUP BY student_name;