DISTINCT can be used only once in a SELECT list, and it must precede all column names in that list. : DISTINCT « Query « SQL Server / T-SQL Tutorial






the DISTINCT clause displays all rows where the combination of columns is distinct.

9> CREATE TABLE employee(
10>    id          INTEGER NOT NULL PRIMARY KEY,
11>    first_name  VARCHAR(10),
12>    last_name   VARCHAR(10),
13>    salary      DECIMAL(10,2),
14>    start_Date  DATETIME,
15>    region      VARCHAR(10),
16>    city        VARCHAR(20),
17>    managerid   INTEGER
18> );
19> 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> select distinct region from employee;
3> GO
region
----------
East
North
South
West

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








1.12.DISTINCT
1.12.1.A SELECT statement that eliminates duplicate rows
1.12.2.A summary query that uses the DISTINCT keyword
1.12.3.When the DISTINCT keyword is used, all duplicate values are eliminated before the function COUNT is applied.
1.12.4.Distinct with two columns
1.12.5.DISTINCT can be used only once in a SELECT list, and it must precede all column names in that list.
1.12.6.Correlated subquery using Distinct
1.12.7.Using SELECT DISTINCT or a GROUP BY statement in the inner query