How to count records in SQL - sql

Question

Edit: Schema taken/extrapolated from comment below
create table #employees
(
Emp_ID int,
Name varchar(50),
Dept_ID int,
);
create table #departments
(
Dept_ID int,
Dept_Name varchar(50)
);
How do I count the number of employees from table employees that work in each department in table departments and include all departments that have no employees working in them.

Answer 1

Welcome to SO.
This problem is quite simple to solve. The steps would be as follows:
Join the Departments table to the Employees table on the Dept_ID column.
SELECT the Dept_ID and Count() and GROUP BY the Dept_ID field.
In order to return Departments without employees you need to LEFT JOIN this aggregation to the Departments table on the Dept_ID column.
In order to return the value of 0 for departments without employees, use the ISNULL() function.
Please see the below sample script using your schema. Note that this script is written in T-SQL, as you did not mention your server type.
create table #employees
(
Emp_ID int,
Name varchar(50),
Dept_ID int,
);
create table #departments
(
Dept_ID int,
Dept_Name varchar(50)
);
insert into #employees
select 1, 'Pim', 1
union all
select 2, 'Salma', 2;
insert into #departments
select 1, 'IT'
union all
select 2, 'Marketing'
union all
select 3, 'Design'
select
d1.Dept_Name
,isnull(d2.EmployeeCount, 0) as EmployeeCount
from
#departments d1
left join
(
select
d.Dept_ID
,count(e.Dept_ID) as EmployeeCount
from
#departments d
join
#employees e
on e.Dept_ID = d.Dept_ID
group by
d.Dept_ID
)
d2
on d2.Dept_ID = d1.Dept_ID
drop table #employees
drop table #departments

Answer 2

As you have supplied no data please try below and see if this works for you
Create the tables, I don't know if this is similar to your table structure
CREATE TABLE tbl_EMPLOYEES (Empl_Name nvarchar(20), Dept nvarchar(15))
CREATE TABLE tbl_DEPARTMENT (Dept nvarchar(15))
Populate these tables
INSERT INTO tbl_EMPLOYEES Values ('James', 'Finance')
INSERT INTO tbl_EMPLOYEES Values ('Tim', 'HR')
INSERT INTO tbl_EMPLOYEES Values ('Sally', 'Finance')
INSERT INTO tbl_EMPLOYEES Values ('Bob', 'Sales')
INSERT INTO tbl_EMPLOYEES Values ('Sam', 'HR')
INSERT INTO tbl_EMPLOYEES Values ('James', 'Finance')
INSERT INTO tbl_DEPARTMENT Values ('Finance')
INSERT INTO tbl_DEPARTMENT Values ('HR')
INSERT INTO tbl_DEPARTMENT Values ('Sales')
INSERT INTO tbl_DEPARTMENT Values ('IT')
This query will give you the number of people in each department
SELECT Dept, Count(Dept) AS Count
FROM
(
SELECT Dept
FROM tbl_EMPLOYEES
) AS Blah_Blah
GROUP BY Dept