Count employees in the same department : COUNT « Aggregate Functions « Oracle PL/SQL Tutorial

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Oracle PL/SQL Tutorial » Aggregate Functions » COUNT 
12. 3. 9. Count employees in the same department
SQL>
SQL>
SQL> create table employees(
  2    empno      NUMBER(4)
  3  , ename      VARCHAR2(8)
  4  , init       VARCHAR2(5)
  5  , job        VARCHAR2(8)
  6  , mgr        NUMBER(4)
  7  , bdate      DATE
  8  , msal       NUMBER(6,2)
  9  , comm       NUMBER(6,2)
 10  , deptno     NUMBER(2) ) ;

Table created.

SQL>
SQL>
SQL> insert into employees values(1,'Jason',  'N',  'TRAINER', 2,   date '1965-12-18',  800 , NULL,  10);

row created.

SQL> insert into employees values(2,'Jerry',  'J',  'SALESREP',3,   date '1966-11-19',  1600300,   10);

row created.

SQL> insert into employees values(3,'Jord',   'T' 'SALESREP',4,   date '1967-10-21',  1700500,   20);

row created.

SQL> insert into employees values(4,'Mary',   'J',  'MANAGER', 5,   date '1968-09-22',  1800, NULL,  20);

row created.

SQL> insert into employees values(5,'Joe',    'P',  'SALESREP',6,   date '1969-08-23',  19001400,  30);

row created.

SQL> insert into employees values(6,'Black',  'R',  'MANAGER', 7,   date '1970-07-24',  2000, NULL,  30);

row created.

SQL> insert into employees values(7,'Red',    'A',  'MANAGER', 8,   date '1971-06-25',  2100, NULL,  40);

row created.

SQL> insert into employees values(8,'White',  'S',  'TRAINER', 9,   date '1972-05-26',  2200, NULL,  40);

row created.

SQL> insert into employees values(9,'Yellow', 'C',  'DIRECTOR',10,  date '1973-04-27',  2300, NULL,  20);

row created.

SQL> insert into employees values(10,'Pink',  'J',  'SALESREP',null,date '1974-03-28',  24000,     30);

row created.

SQL>
SQL>
SQL> create table departments
  2  deptno NUMBER(2)
  3  , dname  VARCHAR2(10)
  4  , location VARCHAR2(20)
  5  , mgr    NUMBER(4)
  6  ;

Table created.

SQL>
SQL> insert into departments values (10,'ACCOUNTING','NEW YORK' ,  2);

row created.

SQL> insert into departments values (20,'TRAINING',  'VANCOUVER',  3);

row created.

SQL> insert into departments values (30,'SALES',     'CHICAGO',    4);

row created.

SQL> insert into departments values (40,'HR',        'BOSTON',     5);

row created.

SQL>
SQL>
SQL>
SQL> select deptno, count(e.empno)
  2  from   employees e
  3         right outer join
  4         departments d
  5         using (deptno)
  6  group  by deptno;

    DEPTNO COUNT(E.EMPNO)
---------- --------------
        30              3
        20              3
        40              2
        10              2

SQL>
SQL>
SQL> drop table employees;

Table dropped.

SQL>
SQL> drop table departments;

Table dropped.

SQL>
SQL>
12. 3. COUNT
12. 3. 1. COUNT(x) gets the number of rows returned by a query.
12. 3. 2. Passes ROWID to COUNT() and gets the number of rows
12. 3. 3. COUNT() with null
12. 3. 4. Using an aggregate with the GROUP BY clause to count by city
12. 3. 5. COUNT(1) from a table
12. 3. 6. Count column with table alias
12. 3. 7. Count distinct column value
12. 3. 8. Compare the difference between count(*) and count(distinct course)
12. 3. 9. Count employees in the same department
12. 3. 10. JOIN with AND and aggregate function
12. 3. 11. count(*) - count(onhand)
12. 3. 12. count(*) vs count(column name)
12. 3. 13. Count all employees by even/odd employee id
12. 3. 14. Count date field value, and calculation
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