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