SQL Server/T-SQL/Constraints/Unique

Adding a UNIQUE Constraint to an Existing Table

 
125>
126> CREATE TABLE employee(
127>    id          INTEGER NOT NULL PRIMARY KEY,
128>    first_name  VARCHAR(10),
129>    last_name   VARCHAR(10),
130>    salary      DECIMAL(10,2),
131>    start_Date  DATETIME,
132>    region      VARCHAR(10),
133>    city        VARCHAR(20),
134>    managerid   INTEGER
135> );
136> 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 2" ,  "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 2    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> ALTER TABLE employee
4> ADD CONSTRAINT UNQ_Name
5> UNIQUE (first_Name)
6> GO
1>
2>
3>
4>
5> drop table employee;
6> GO
1>

Add Unique constaint to table creation

17>
18> -- Add Unique constaint to table creation
19> CREATE TABLE projects (project_no   CHAR(4)  DEFAULT "p1",
20>                        project_name CHAR(15) NOT NULL,
21>                        budget       FLOAT    NULL
22>                        CONSTRAINT   unique_no UNIQUE (project_no))
23> GO
1>
2> drop table projects
3> GO
1>

A unique constraint

 

5> CREATE TABLE MyTable (
6>   MyID Int IDENTITY(1,1) NOT NULL , ID Int NOT NULL
7>  , Description nVarChar(50)
8>  , Region nVarChar(10) DEFAULT "PNW"
9>  , CONSTRAINT MyTable_PK PRIMARY KEY NONCLUSTERED (MyID,ID))
10> GO
1>
2> drop table MyTable;
3> GO