Group by clause and Having clause In Sql Server

group by clause:-                                                                                                                                    
When we run aggregated function in select query,we get the output on the basis of all the records but if we want to use aggregated function,then we should give us output on the basis of group and column and we can used 'group by clause' before  grouping the records.If we want to keep some conditions,we can specify 'where' clause and after grouping the records if we want to some conditions then we can use 'having' clause.
There are some commands to explain the group by clause. which are given below:
1. ) First create a students table as shown below:

2. )  Use group by command as given below:
 
   select deptName,count(*) from students where salary>1000
   group by deptName
Output:-

3. ) Use group by and Having clause as given below:-

     select deptName,count(*) from students 
    group by deptName
    having COUNT(*)>1
 Output:-

4. ) Use group by , where clause and having clause as given below:-

      select deptName,count(*)as Total from students where salary >=300
      group by deptName
      having COUNT(*)>1
Output:-