count(*) vs count(column name) : COUNT « Aggregate Functions « Oracle PL / SQL






count(*) vs count(column name)

  
SQL>
SQL> CREATE TABLE emp (
  2    emp_id               NUMBER,
  3    ename             VARCHAR2(40),
  4    hire_date        DATE DEFAULT sysdate,
  5    end_date DATE,
  6    rate     NUMBER(5,2),
  7    CONSTRAINT emp_pk    PRIMARY KEY (emp_id)
  8  );

Table created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (101, 'Mary', to_date('15-Nov-1961','dd-mon-yyyy'),null,169);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (102, 'Tom', to_date('16-Sep-1964','dd-mon-yyyy'),to_date('5-May-2004','dd-mon-yyyy'),135);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (104, 'Peter', to_date('29-Dec-1987','dd-mon-yyyy'),to_date('1-Apr-2004','dd-mon-yyyy'),99);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (105, 'Mike', to_date('15-Jun-2004','dd-mon-yyyy'),null,121);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (107, 'Less', to_date('2-Jan-2004','dd-mon-yyyy'),null,45);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (108, 'Park', to_date('1-Mar-1994','dd-mon-yyyy'),to_date('15-Nov-2004','dd-mon-yyyy'),220);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (110, 'Ink', to_date('4-Apr-2004','dd-mon-yyyy'),to_date('30-Sep-2004','dd-mon-yyyy'),84);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (111, 'Tike', to_date('23-Aug-1976','dd-mon-yyyy'),null,100);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (112, 'Inn', to_date('15-Nov-1961','dd-mon-yyyy'),to_date('4-Apr-2004','dd-mon-yyyy'),70);

1 row created.

SQL> INSERT INTO emp(emp_id, ename, hire_date,end_date, rate)VALUES (113, 'Kate', to_date('3-Mar-2004','dd-mon-yyyy'),to_date('31-Oct-2004','dd-mon-yyyy'),300);

1 row created.

SQL>
SQL> SET ECHO ON
SQL> SELECT COUNT(*), COUNT(end_date)
  2  FROM emp;
        10               6

1 row selected.

SQL>
SQL>
SQL> drop table emp;

Table dropped.

   
    
  








Related examples in the same category

1.COUNT(column) and COUNT(*): count the number of rows passed into the function.
2.Syntax: COUNT([DISTINCT]|[ALL] )
3.Using GROUP BY would tell us how many cars from each vendor we have on the lot:
4.Find out which maker has a null value car with count()
5.-Using the COUNT function in Having clause
6.Example using the COUNT function with group by clause
7.Count with group by: count for a group value
8.Get the number of rows in each city group using the COUNT() function
9.count null
10.Column alias name for count function
11.Count(*) - count(column_Name)
12.count distinct column value
13.count(1)
14.count(distinct state)
15.Count(*) and column renaming
16.Count() with where clause
17.Count date field value, and calculation
18.Count department and calculate average salary
19.Count employee in a department after grouping by department id
20.Count employee, group by department id and job title
21.count(*) - count(onhand)