The COUNT(*) function ignores NULL values
3>
4> CREATE TABLE employee(
5> id INTEGER NOT NULL PRIMARY KEY,
6> first_name VARCHAR(10),
7> last_name VARCHAR(10),
8> salary DECIMAL(10,2),
9> start_Date DATETIME,
10> region VARCHAR(10),
11> city VARCHAR(20),
12> managerid INTEGER
13> );
14> GO
1> INSERT INTO employee VALUES (1, 'Jason' , 'Martin', 5890,'2005-03-22','North','Vancouver',3);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (2, 'Alison', 'Mathews',4789,'2003-07-21','South','Utown',4);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (3, 'James' , 'Smith', 6678,'2001-12-01','North','Paris',5);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (4, 'Celia' , 'Rice', 5567,'2006-03-03','South','London',6);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (5, 'Robert', 'Black', 4467,'2004-07-02','East','Newton',7);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (6, 'Linda' , 'Green' , 6456,'2002-05-19','East','Calgary',8);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (7, 'David' , 'Larry', 5345,'2008-03-18','West','New York',9);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (8, 'James' , 'Cat', 4234,'2007-07-17','West','Regina',9);
2> GO
(1 rows affected)
1> INSERT INTO employee VALUES (9, NULL , 'Act', 6123,'2001-04-16','North','Toronto',10);
2> GO
(1 rows affected)
1>
2> select * from employee;
3> GO
id first_name last_name salary start_Date region city managerid
----------- ---------- ---------- ------------ ----------------------- ---------- -------------------- -----------
1 Jason Martin 5890.00 2005-03-22 00:00:00.000 North Vancouver 3
2 Alison Mathews 4789.00 2003-07-21 00:00:00.000 South Utown 4
3 James Smith 6678.00 2001-12-01 00:00:00.000 North Paris 5
4 Celia Rice 5567.00 2006-03-03 00:00:00.000 South London 6
5 Robert Black 4467.00 2004-07-02 00:00:00.000 East Newton 7
6 Linda Green 6456.00 2002-05-19 00:00:00.000 East Calgary 8
7 David Larry 5345.00 2008-03-18 00:00:00.000 West New York 9
8 James Cat 4234.00 2007-07-17 00:00:00.000 West Regina 9
9 NULL Act 6123.00 2001-04-16 00:00:00.000 North Toronto 10
(9 rows affected)
1>
2>
3>
4> SELECT COUNT(First_Name) FROM Employee
5> SELECT COUNT(*) FROM Employee
6>
7>
8> drop table employee;
9> GO
-----------
8
Warning: Null value is eliminated by an aggregate or other SET operation.
-----------
9
(1 rows affected)
1>
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