Answers for "how to use group by in sql"

what is group function in sql

--- GROUP FUNCTION | MULTI ROW FUNCTION | AGGREGATE FUNCTION 
--- COUNT , MAX , MIN , SUM , AVG

group by clause in ms sql

/*Group by clause is used to group a selected  set of rows into a set of summary 
rows by the values of one or more column or expression. It is always used in
Conjunction with one or more aggregate function.*/
SELECT AGGREGATE_FUNCTION(Column_Name) FROM Table_Name
/*Group by exmaple*/
SELECT city, sum(Salary) as TotalSalary FROM tblEmployee GROUP BY City

group by

SELECT
  <column_name>,
  COUNT(<column_name>) AS `value_occurrence` 

FROM
  <my_table>

GROUP BY 
  <column_name>

ORDER BY 
  `value_occurrence` DESC

LIMIT 1;

group by

class groupby(object):
    # [k for k, g in groupby('AAAABBBCCDAABBB')] --> A B C D A B
    # [list(g) for k, g in groupby('AAAABBBCCD')] --> AAAA BBB CC D
    def __init__(self, iterable, key=None):
        if key is None:
            key = lambda x: x
        self.keyfunc = key
        self.it = iter(iterable)
        self.tgtkey = self.currkey = self.currvalue = object()
    def __iter__(self):
        return self
    def next(self):
        while self.currkey == self.tgtkey:
            self.currvalue = next(self.it)    # Exit on StopIteration
            self.currkey = self.keyfunc(self.currvalue)
        self.tgtkey = self.currkey
        return (self.currkey, self._grouper(self.tgtkey))
    def _grouper(self, tgtkey):
        while self.currkey == tgtkey:
            yield self.currvalue
            self.currvalue = next(self.it)    # Exit on StopIteration
            self.currkey = self.keyfunc(self.currvalue)

GROUP BY

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

group functions in sql

Multiple Row Functions (Group functions, Aggregate functions):
(Count, MIN , MAX, AVG, SUM)
will run for multiple rows and return a single value