SQL Server/T-SQL Tutorial/Aggregate Functions/Count — различия между версиями
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Версия 13:46, 26 мая 2010
Содержание
- 1 A common mistake with DISTINCT is to code the DISTINCT statement before the COUNT statement.
- 2 Count function with column alias
- 3 Counting unique values.
- 4 Counting values including NULL values.
- 5 COUNT(*) returns the total count of all records (rows) in the column, including NULL values of selected records by the query.
- 6 COUNT returns the total count of records in a column or the count for DISTINCT (unique) values selected by the query.
- 7 Count table row in dynamic sql
- 8 Using ISNULL to count all values including NULLs.
A common mistake with DISTINCT is to code the DISTINCT statement before the COUNT statement.
Because each row counted is already unique, DISTINCT will have no impact.
5>
6>
7> CREATE TABLE CD (
8> CD_ID integer NOT NULL PRIMARY KEY,
9> CD_Title varchar(40),
10> Composer_ID integer NOT NULL,
11> Classif_ID integer NOT NULL,
12> SalesPrice money,
13> AverageCost money)
14> GO
1> INSERT into CD VALUES(2000,"John",100,1,16.99,6.99)
2> INSERT into CD VALUES(2001,"Chicago 16",107,1,14.99,5.99)
3> INSERT into CD VALUES(2002,"Chicago 17",107,1,14.99,5.99)
4> INSERT into CD VALUES(2003,"Chicago 18",107,1,14.99,5.99)
5> INSERT into CD VALUES(2004,"Greatest Hits",107,1,16.99,7.99)
6> INSERT into CD VALUES(2005,"Midnight",101,3,14.99,5.99)
7> INSERT into CD VALUES(2006,"Mode",115,3,14.99,5.99)
8> INSERT into CD VALUES(2007,"Ultra",115,3,15.99,5.99)
9> INSERT into CD VALUES(2008,"Mindcrime",102,4,14.99,5.99)
10> INSERT into CD VALUES(2009,"Empire",102,4,14.99,5.99)
11> INSERT into CD VALUES(2010,"Land",102,4,12.99,4.99)
12> INSERT into CD VALUES(2011,"Night",103,4,11.99,3.99)
13> INSERT into CD VALUES(2012,"Pyromania",103,4,14.99,5.99)
14> INSERT into CD VALUES(2013,"Hysteria",103,4,14.99,5.99)
15> INSERT into CD VALUES(2014,"Hits",103,4,13.99,4.99)
16> INSERT into CD VALUES(2015,"Hits 2",104,2,15.99,6.99)
17> INSERT into CD VALUES(2016,"Greatest",105,2,14.99,5.99)
18> INSERT into CD VALUES(2017,"Hits 3",106,1,13.99,5.99)
19> INSERT into CD VALUES(2018,"Deep",108,1,12.99,2.99)
20> INSERT into CD VALUES(2019,"Turning",109,1,14.99,5.99)
21> INSERT into CD VALUES(2020,"TheHits",109,1,16.99,7.99)
22> INSERT into CD VALUES(2021,"Cars",110,1,9.99,3.99)
23> INSERT into CD VALUES(2022,"Anthology",110,1,25.99,11.99)
24> INSERT into CD VALUES(2023,"City",110,1,14.99,5.99)
25> INSERT into CD VALUES(2024,"Rick",111,1,11.99,2.99)
26> INSERT into CD VALUES(2025,"Live",112,1,19.99,8.99)
27> INSERT into CD VALUES(2026,"Pat",113,1,16.99,6.99)
28> INSERT into CD VALUES(2027,"Big",114,1,14.99,5.99)
29> INSERT into CD VALUES(2028,"Hurting",114,1,11.99,3.99)
30> INSERT into CD VALUES(2029,"Vol 1",116,1,9.99,2.99)
31> INSERT into CD VALUES(2030,"Vol 2",116,1,9.99,2.99)
32> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
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1>
2>
3> SELECT DISTINCT COUNT(Classif_ID) from CD
4> GO
-----------
31
(1 rows affected)
1>
2> drop table CD;
3> GO
Count function with column alias
5>
6> create table Billings (
7> BankerID INTEGER,
8> BillingNumber INTEGER,
9> BillingDate datetime,
10> BillingTotal INTEGER,
11> TermsID INTEGER,
12> BillingDueDate datetime ,
13> PaymentTotal INTEGER,
14> CreditTotal INTEGER
15>
16> );
17> GO
1>
2> INSERT INTO Billings VALUES (1, 1, "2005-01-22", 165, 1,"2005-04-22",123,321);
3> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (2, 2, "2001-02-21", 165, 1,"2002-02-22",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (3, 3, "2003-05-02", 165, 1,"2005-04-12",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (4, 4, "1999-03-12", 165, 1,"2005-04-18",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (5, 5, "2000-04-23", 165, 1,"2005-04-17",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (6, 6, "2001-06-14", 165, 1,"2005-04-18",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (7, 7, "2002-07-15", 165, 1,"2005-04-19",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (8, 8, "2003-08-16", 165, 1,"2005-04-20",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (9, 9, "2004-09-17", 165, 1,"2005-04-21",123,321);
2> GO
(1 rows affected)
1> INSERT INTO Billings VALUES (0, 0, "2005-10-18", 165, 1,"2005-04-22",123,321);
2> GO
(1 rows affected)
1>
2>
3> SELECT COUNT(*) AS NumberOfBillings,
4> SUM(BillingTotal - PaymentTotal - CreditTotal) AS TotalDue
5> FROM Billings
6> WHERE BillingTotal - PaymentTotal - CreditTotal > 0
7> GO
NumberOfBillings TotalDue
---------------- -----------
0 NULL
(1 rows affected)
1>
2> drop table Billings;
3> GO
Counting unique values.
7> CREATE TABLE CD (
8> CD_ID integer NOT NULL PRIMARY KEY,
9> CD_Title varchar(40),
10> Composer_ID integer NOT NULL,
11> Classif_ID integer NOT NULL,
12> SalesPrice money,
13> AverageCost money)
14> GO
1> INSERT into CD VALUES(2000,"John",100,1,16.99,6.99)
2> INSERT into CD VALUES(2001,"Chicago 16",107,1,14.99,5.99)
3> INSERT into CD VALUES(2002,"Chicago 17",107,1,14.99,5.99)
4> INSERT into CD VALUES(2003,"Chicago 18",107,1,14.99,5.99)
5> INSERT into CD VALUES(2004,"Greatest Hits",107,1,16.99,7.99)
6> INSERT into CD VALUES(2005,"Midnight",101,3,14.99,5.99)
7> INSERT into CD VALUES(2006,"Mode",115,3,14.99,5.99)
8> INSERT into CD VALUES(2007,"Ultra",115,3,15.99,5.99)
9> INSERT into CD VALUES(2008,"Mindcrime",102,4,14.99,5.99)
10> INSERT into CD VALUES(2009,"Empire",102,4,14.99,5.99)
11> INSERT into CD VALUES(2010,"Land",102,4,12.99,4.99)
12> INSERT into CD VALUES(2011,"Night",103,4,11.99,3.99)
13> INSERT into CD VALUES(2012,"Pyromania",103,4,14.99,5.99)
14> INSERT into CD VALUES(2013,"Hysteria",103,4,14.99,5.99)
15> INSERT into CD VALUES(2014,"Hits",103,4,13.99,4.99)
16> INSERT into CD VALUES(2015,"Hits 2",104,2,15.99,6.99)
17> INSERT into CD VALUES(2016,"Greatest",105,2,14.99,5.99)
18> INSERT into CD VALUES(2017,"Hits 3",106,1,13.99,5.99)
19> INSERT into CD VALUES(2018,"Deep",108,1,12.99,2.99)
20> INSERT into CD VALUES(2019,"Turning",109,1,14.99,5.99)
21> INSERT into CD VALUES(2020,"TheHits",109,1,16.99,7.99)
22> INSERT into CD VALUES(2021,"Cars",110,1,9.99,3.99)
23> INSERT into CD VALUES(2022,"Anthology",110,1,25.99,11.99)
24> INSERT into CD VALUES(2023,"City",110,1,14.99,5.99)
25> INSERT into CD VALUES(2024,"Rick",111,1,11.99,2.99)
26> INSERT into CD VALUES(2025,"Live",112,1,19.99,8.99)
27> INSERT into CD VALUES(2026,"Pat",113,1,16.99,6.99)
28> INSERT into CD VALUES(2027,"Big",114,1,14.99,5.99)
29> INSERT into CD VALUES(2028,"Hurting",114,1,11.99,3.99)
30> INSERT into CD VALUES(2029,"Vol 1",116,1,9.99,2.99)
31> INSERT into CD VALUES(2030,"Vol 2",116,1,9.99,2.99)
32> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
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1>
2>
3> SELECT COUNT(DISTINCT Classif_ID) from CD
4> GO
-----------
4
(1 rows affected)
1>
2> drop table CD;
3> GO
Counting values including NULL values.
5> CREATE TABLE CD (
6> CD_ID integer NOT NULL PRIMARY KEY,
7> CD_Title varchar(40),
8> Composer_ID integer NOT NULL,
9> Classif_ID integer NOT NULL,
10> SalesPrice money,
11> AverageCost money)
12> GO
1> INSERT into CD VALUES(2000,"John",100,1,16.99,6.99)
2> INSERT into CD VALUES(2001,"Chicago 16",107,1,14.99,5.99)
3> INSERT into CD VALUES(2002,"Chicago 17",107,1,14.99,5.99)
4> INSERT into CD VALUES(2003,"Chicago 18",107,1,14.99,5.99)
5> INSERT into CD VALUES(2004,"Greatest Hits",107,1,16.99,7.99)
6> INSERT into CD VALUES(2005,"Midnight",101,3,14.99,5.99)
7> INSERT into CD VALUES(2006,"Mode",115,3,14.99,5.99)
8> INSERT into CD VALUES(2007,"Ultra",115,3,15.99,5.99)
9> INSERT into CD VALUES(2008,"Mindcrime",102,4,14.99,5.99)
10> INSERT into CD VALUES(2009,"Empire",102,4,14.99,5.99)
11> INSERT into CD VALUES(2010,"Land",102,4,12.99,4.99)
12> INSERT into CD VALUES(2011,"Night",103,4,11.99,3.99)
13> INSERT into CD VALUES(2012,"Pyromania",103,4,14.99,5.99)
14> INSERT into CD VALUES(2013,"Hysteria",103,4,14.99,5.99)
15> INSERT into CD VALUES(2014,"Hits",103,4,13.99,4.99)
16> INSERT into CD VALUES(2015,"Hits 2",104,2,15.99,6.99)
17> INSERT into CD VALUES(2016,"Greatest",105,2,14.99,5.99)
18> INSERT into CD VALUES(2017,"Hits 3",106,1,13.99,5.99)
19> INSERT into CD VALUES(2018,"Deep",108,1,12.99,2.99)
20> INSERT into CD VALUES(2019,"Turning",109,1,14.99,5.99)
21> INSERT into CD VALUES(2020,"TheHits",109,1,16.99,7.99)
22> INSERT into CD VALUES(2021,"Cars",110,1,9.99,3.99)
23> INSERT into CD VALUES(2022,"Anthology",110,1,25.99,11.99)
24> INSERT into CD VALUES(2023,"City",110,1,14.99,5.99)
25> INSERT into CD VALUES(2024,"Rick",111,1,11.99,2.99)
26> INSERT into CD VALUES(2025,"Live",112,1,19.99,8.99)
27> INSERT into CD VALUES(2026,"Pat",113,1,16.99,6.99)
28> INSERT into CD VALUES(2027,"Big",114,1,14.99,5.99)
29> INSERT into CD VALUES(2028,"Hurting",114,1,11.99,3.99)
30> INSERT into CD VALUES(2029,"Vol 1",116,1,9.99,2.99)
31> INSERT into CD VALUES(2030,"Vol 2",116,1,9.99,2.99)
32> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
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(1 rows affected)
1>
2>
3> SELECT COUNT(*) from CD
4> GO
-----------
31
(1 rows affected)
1>
2> drop table CD;
3> GO
COUNT(*) returns the total count of all records (rows) in the column, including NULL values of selected records by the query.
DISTINCT is not allowed with this function.
5>
6>
7>
8> CREATE TABLE sales(
9> stor_id char(4) NOT NULL,
10> ord_num varchar(20) NOT NULL,
11> ord_date datetime NOT NULL,
12> qty smallint NOT NULL,
13> payterms varchar(12) NOT NULL,
14> title_id varchar(80)
15> )
16> GO
1> insert sales values("1", "QA7442.3", "09/13/94", 75, "ON Billing","1")
2> insert sales values("2", "D4482", "09/14/94", 10, "Net 60", "1")
3> insert sales values("3", "N914008", "09/14/94", 20, "Net 30", "2")
4> insert sales values("4", "N914014", "09/14/94", 25, "Net 30", "3")
5> insert sales values("5", "423LL922", "09/14/94", 15, "ON Billing","3")
6> insert sales values("6", "423LL930", "09/14/94", 10, "ON Billing","2")
7> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
1>
2>
3> select COUNT(*) from sales;
4> GO
-----------
6
(1 rows affected)
1>
2> drop table sales;
3>
4> GO
COUNT returns the total count of records in a column or the count for DISTINCT (unique) values selected by the query.
All NULL values are ignored in the total count.
9> CREATE TABLE sales(
10> stor_id char(4) NOT NULL,
11> ord_num varchar(20) NOT NULL,
12> ord_date datetime NOT NULL,
13> qty smallint NOT NULL,
14> payterms varchar(12) NOT NULL,
15> title_id varchar(80)
16> )
17> GO
1> insert sales values("1", "QA7442.3", "09/13/94", 75, "ON Billing","1")
2> insert sales values("2", "D4482", "09/14/94", 10, "Net 60", "1")
3> insert sales values("3", "N914008", "09/14/94", 20, "Net 30", "2")
4> insert sales values("4", "N914014", "09/14/94", 25, "Net 30", "3")
5> insert sales values("5", "423LL922", "09/14/94", 15, "ON Billing","3")
6> insert sales values("6", "423LL930", "09/14/94", 10, "ON Billing","2")
7> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
1>
2>
3> select COUNT(qty) from sales;
4> GO
-----------
6
(1 rows affected)
1>
2> drop table sales;
3>
4> GO
1>
Count table row in dynamic sql
3> CREATE TABLE Orders (
4> OrderID int IDENTITY (1, 1) NOT NULL ,
5> CustomerID nchar (5) NULL ,
6> EmployeeID int NULL ,
7> OrderDate datetime NULL ,
8> RequiredDate datetime NULL ,
9> ShippedDate datetime NULL ,
10> ShipVia int NULL ,
11> Freight money NULL DEFAULT (0),
12> ShipName nvarchar (40) NULL ,
13> ShipAddress nvarchar (60) NULL ,
14> ShipCity nvarchar (15) NULL ,
15> ShipRegion nvarchar (15) NULL ,
16> ShipPostalCode nvarchar (10) NULL ,
17> ShipCountry nvarchar (15) NULL
18> )
19> GO
1>
2> DECLARE @schemaname AS NVARCHAR(128), @tablename AS NVARCHAR(128);
3> SET @schemaname = N"dbo";
4> SET @tablename = N"Orders";
5>
6> DECLARE @objectname AS NVARCHAR(517);
7> SET @objectname = QUOTENAME(@schemaname) + N"." + QUOTENAME(@tablename);
8> EXEC(N"SELECT COUNT(*) FROM " + @objectname + N";");
9> GO
-----------
0
1>
2> drop table orders;
3> GO
Using ISNULL to count all values including NULLs.
6>
7> CREATE TABLE CD (
8> CD_ID integer NOT NULL PRIMARY KEY,
9> CD_Title varchar(40),
10> Composer_ID integer NOT NULL,
11> Classif_ID integer NOT NULL,
12> SalesPrice money,
13> AverageCost money)
14> GO
1> INSERT into CD VALUES(2000,"John",100,1,16.99,6.99)
2> INSERT into CD VALUES(2001,"Chicago 16",107,1,14.99,5.99)
3> INSERT into CD VALUES(2002,"Chicago 17",107,1,14.99,5.99)
4> INSERT into CD VALUES(2003,"Chicago 18",107,1,14.99,5.99)
5> INSERT into CD VALUES(2004,"Greatest Hits",107,1,16.99,7.99)
6> INSERT into CD VALUES(2005,"Midnight",101,3,14.99,5.99)
7> INSERT into CD VALUES(2006,"Mode",115,3,14.99,5.99)
8> INSERT into CD VALUES(2007,"Ultra",115,3,15.99,5.99)
9> INSERT into CD VALUES(2008,"Mindcrime",102,4,14.99,5.99)
10> INSERT into CD VALUES(2009,"Empire",102,4,14.99,5.99)
11> INSERT into CD VALUES(2010,"Land",102,4,12.99,4.99)
12> INSERT into CD VALUES(2011,"Night",103,4,11.99,3.99)
13> INSERT into CD VALUES(2012,"Pyromania",103,4,14.99,5.99)
14> INSERT into CD VALUES(2013,"Hysteria",103,4,14.99,5.99)
15> INSERT into CD VALUES(2014,"Hits",103,4,13.99,4.99)
16> INSERT into CD VALUES(2015,"Hits 2",104,2,15.99,6.99)
17> INSERT into CD VALUES(2016,"Greatest",105,2,14.99,5.99)
18> INSERT into CD VALUES(2017,"Hits 3",106,1,13.99,5.99)
19> INSERT into CD VALUES(2018,"Deep",108,1,12.99,2.99)
20> INSERT into CD VALUES(2019,"Turning",109,1,14.99,5.99)
21> INSERT into CD VALUES(2020,"TheHits",109,1,16.99,7.99)
22> INSERT into CD VALUES(2021,"Cars",110,1,9.99,3.99)
23> INSERT into CD VALUES(2022,"Anthology",110,1,25.99,11.99)
24> INSERT into CD VALUES(2023,"City",110,1,14.99,5.99)
25> INSERT into CD VALUES(2024,"Rick",111,1,11.99,2.99)
26> INSERT into CD VALUES(2025,"Live",112,1,19.99,8.99)
27> INSERT into CD VALUES(2026,"Pat",113,1,16.99,6.99)
28> INSERT into CD VALUES(2027,"Big",114,1,14.99,5.99)
29> INSERT into CD VALUES(2028,"Hurting",114,1,11.99,3.99)
30> INSERT into CD VALUES(2029,"Vol 1",116,1,9.99,2.99)
31> INSERT into CD VALUES(2030,"Vol 2",116,1,9.99,2.99)
32> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
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(1 rows affected)
1>
2>
3> SELECT COUNT(ISNULL(MI,"")) from Store
4> GO
Msg 208, Level 16, State 1, Server J\SQLEXPRESS, Line 3
Invalid object name "Store".
1>
2> drop table CD;
3> GO