what this constrain meaning ?

Question

I work on sql server 2012 i see constrain but i don't know what is meaning

ALTER TABLE [Parts].[TradeCodes] ADD  CONSTRAINT [UC_PartCode] UNIQUE NONCLUSTERED 
(
    [PartID] ASC,
    [CodeTypeID] ASC,
    [PartLevel] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO

so what is benefit from code above

Answer 1

That is the unique constraint so that the combination of those three columns should be unique. It is not allowed to have the duplicates. See UNIQUE Constraints for more details.

Answer 2

Hi @ahmed salah ,

Constraints in SQL Server are predefined rules and restrictions that are enforced in a single column or multiple columns, regarding the values allowed in the columns, to maintain the integrity, accuracy, and reliability of that column’s data.

In other words, if the inserted data meets the constraint rule, it will be inserted successfully. If the inserted data violates the defined constraint, the insert operation will be aborted.

There are six main constraints:

• SQL NOT NULL
• UNIQUE
• PRIMARY KEY
• FOREIGN KEY
• CHECK
• DEFAULT

In your example, it could be UNIQUE constraint.

The UNIQUE constraint in SQL Server ensures that you do not have duplicate values in a single column or combination of columns. These columns should be part of the UNIQUE constraints.

[PartID] ASC,
[CodeTypeID] ASC,
[PartLevel] ASC

So your constraint was added to make sure that the combination of above three columns should be unique, otherwise it could report errors.

Best regards,
Melissa

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