group by sql

# Say you have a table called SALARIES that contains a 
# few duplicate NAME entries...
+----+-------------+--------+
| ID |    NAME     | SALARY |
+----+-------------+--------+
| 1	 |     Bob     |  500   |
| 2  |    Alice    |  500   |
| 3  |    Alice    |  200   |
| 4  |    Frank    |  700   |
| 5  |    Percy    |  100   |
| 6  |    Percy    |  800   |
| 7  |   Cyrille   |  400   |
+----+-------------+--------+

# We can obtain the total salaries of each person
# by using GROUP BY in the following query...
SELECT NAME, SALARY FROM SALARIES GROUP BY NAME;

# Which will output the following...
+------------+--------+
|   Alice    |  700   |
|    Bob     |  500   |
|  Cyrille   |  400   |
|   Frank    |  700   |
|   Percy    |  900   |
+------------+--------+

  SELECT column_name(s)
  FROM table_name
  WHERE condition
  GROUP BY column_name(s)
  HAVING condition
  ORDER BY column_name(s); 

SELECT column1, function_name(column2)
FROM table_name
WHERE condition
GROUP BY column1, column2
ORDER BY column1, column2;

function_name: Name of the function used for example, SUM() , AVG().
table_name: Name of the table.
condition: Condition used.

// Use SQL Group By clause after the Where clause
// Any column in the select list must either be in the Group By clause 
// or part of an agregation statement
// Multiple columns can be included in the Group By Clause seperated by a comma
// Multiple columns stipulate the order tree. Order by 
// first column, then second ... etc

Select LastName, FirstName, Sum(LeaveDays), Max(age)
From EmployeeProjects
Where StartDate > '2020-01-01'
Group By LastName, FirstName

SELECT <field1, field2, field3…>
FROM <table1_name>
WHERE <condition/expression>
GROUP BY <field1, field2, field3…>