SQL Server/T-SQL Tutorial/Analytical Functions/STDEV — различия между версиями
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Admin (обсуждение | вклад) м (1 версия) |
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Текущая версия на 10:22, 26 мая 2010
Aggregate Functions STDEV and STDEVP
STDEV computes the standard deviation of all the values listed in a column of expression.
(The standard deviation is computed as the square root of the corresponding variance.)
7> CREATE TABLE employee(
8> id INTEGER NOT NULL PRIMARY KEY,
9> first_name VARCHAR(10),
10> last_name VARCHAR(10),
11> salary DECIMAL(10,2),
12> start_Date DATETIME,
13> region VARCHAR(10),
14> city VARCHAR(20),
15> managerid INTEGER
16> );
17> 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, "Joan" , "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 Joan Act 6123.00 2001-04-16 00:00:00.000 North Toronto 10
(9 rows affected)
1>
2>
3>
4> SELECT STDEV(salary) std_dev_of_budgets
5> FROM employee
6>
7>
8> drop table employee;
9> GO
std_dev_of_budgets
------------------------
869.30016552268989
(1 rows affected)
1>
STDEV() Function is a calculation based on the variance of a numeric range of values.
Actually, it"s simply the square root of the variance.
8> Create Table MyValues (MyValue Float)
9> GO
1>
2> Insert Into MyValues (MyValue) SELECT 2
3> Insert Into MyValues (MyValue) SELECT 3
4> Insert Into MyValues (MyValue) SELECT 4
5> Insert Into MyValues (MyValue) SELECT 5
6> Insert Into MyValues (MyValue) SELECT 6
7> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
1>
2> SELECT VAR(MyValue) FROM MyValues
3> GO
------------------------
2.5
(1 rows affected)
1>
2> SELECT STDEV(MyValue) FROM MyValues
3>
4> drop table MyValues;
5> GO
------------------------
1.5811388300841898
(1 rows affected)
STDEV returns the standard deviation of all the values provided in the expression, based on a sample of the data population.
6>
7> CREATE TABLE employee(
8> id INTEGER NOT NULL PRIMARY KEY,
9> first_name VARCHAR(10),
10> last_name VARCHAR(10),
11> salary DECIMAL(10,2),
12> start_Date DATETIME,
13> region VARCHAR(10),
14> city VARCHAR(20),
15> managerid INTEGER
16> );
17> 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, "Joan" , "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 Joan Act 6123.00 2001-04-16 00:00:00.000 North Toronto 10
(9 rows affected)
1>
2>
3> SELECT STDEV(salary) Variance_salary
4> FROM employee
5> GO
Variance_salary
------------------------
869.30016552268989
(1 rows affected)
1>
2>
3>
4> drop table employee;
5> GO
1>