A common mistake with DISTINCT is to code the DISTINCT statement before the COUNT statement. : Count « Aggregate Functions « SQL Server / T-SQL Tutorial






  1. SQL Server / T-SQL Tutorial
  2. Aggregate Functions
  3. Count
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)

(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)

(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)

(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>
2>
3> SELECT DISTINCT COUNT(Classif_ID) from CD
4> GO

-----------
         31

(1 rows affected)
1>
2> drop table CD;
3> GO








9.3.Count
9.3.1.COUNT returns the total count of records in a column or the count for DISTINCT (unique) values selected by the query.
9.3.2.COUNT(*) returns the total count of all records (rows) in the column, including NULL values of selected records by the query.
9.3.3.Count function with column alias
9.3.4.Counting unique values.
9.3.5.A common mistake with DISTINCT is to code the DISTINCT statement before the COUNT statement.
9.3.6.Counting values including NULL values.
9.3.7.Using ISNULL to count all values including NULLs.
9.3.8.Count table row in dynamic sql