How to add Unique Constraint in SQL table by SQL script

Publié le: 19 février 2019
sur la chaîne: ITSolution

In this video I have shown how to add a Unique Constraint in SQL Server table field by SQL Script.
Suppose I want that in my SQL field every data must be unique and it will be checked just when I want to insert any duplicate data. When anyone want insert duplicate data it will throw an error from database system.
Actually if can be checked from application user interface also it we do it in database level, it will increase database integrity and efficient.

For this case we can set it by creating Unique Constraint by which every data will by checked through the Constraint and will show an error if any duplicated data tried to insert.

These process can be done by two ways: by design view and SQL script.

Here is the Syntax of SQL Script:

When Creating Table:
SYNTAX:
CREATE TABLE TableName
(
Fieldname datatype UNIQUE
)
To set it to multiple field:
CREATE TABLE TableName
(
Fieldname01 datatype,
Fieldname02 datatype,
- - - - - -
Fieldname nth datatype,
CONSTRAINT NameofConstraint UNIQUE (Fieldname01, Fieldname02)
)

After Creating Table: After Creating table unique key can be added by Altering
SYNTAX:

ALTER TABLE Tablename
ADD CONSTRAINT NameOfConstraint UNIQUE (FieldNames);

To Delete/Drop the Constraint :
ALTER TABLE Tablename
DROP CONSTRAINT NameOfConstraint

Here I have shown how to do to do it by design View:
Here is the steps:
1. Create a table
2. Go to design view of table structure
3. Right click then -- Indexes/Keys - - Click Add - - Give a meaning full name – Change type to Unique key - - Select table and Column name and sorting order - - Save the table
4. By Same process we can do it for two field

To delete the unique constraint: Expand Table from Object explorer - - Select Created Constraint under Key Tab – Right mouse -- Delete

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