Group BY: The GROUP BY statement groups rows that have the same values into summary rows, like find the number of customers in each country.The GROUP BY statement is often used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns.
MERGE:The merge statement is used to make changes in one table based on values matched from another.
Also go thorugh https://www.w3schools.com/sql/sql_groupby.asp for simpler understanding
https://www.geeksforgeeks.org/merge-statement-sql-explained/
is there any difference between merge and join in mysql?
And is there any necessary criteria that if you have common field then you can go for join?
let’s consider in case of cross join we don’t need any condition.
“Group By” clause is used for getting aggregate value (example: count of, sum of) in one or more columns with reference to a distinct column in a table. “Order By” clause is used to sort the resulting rows in the order of specified column or columns.
“Group By” and “Order By” can be used together in SQL as shown in the example: SELECT deptno, sum (sal + comm) FROM emp GROUP BY deptno ORDER BY deptno;
This will list the total cost of salary and commission for each department with the list sorted by department number. The example assumes that both “sal” and “comm” have values in every row (non NULL values).