I have the following table:
Create table [dbo].[Medewerker]
(
[Id] int PRIMARY KEY IDENTITY 91,1 NOT NULL,
[Wachtwoord] varchar(50) NOT NULL,
[Rechten] varchar(100) NOT NULL,
[Gebruikersnaam] varchar(30) UNIQUE NOT NULL
)
I'm trying to make it so that the bottom line makes it so that each entry in the "Gebruikersnaam" column is unique. Is what I did right? What do you call this type of feature?
each entry in the "Gebruikersnaam" column is unique
Yes it's right. Essentially what you did is nothing but adding a UNIQUE CONSTRAINT to your column Gebruikersnaam.
Per comment, yes it's better to name your constraint explicitly than let DB engine assign a default name implicitly like
Create table [dbo].[Medewerker]
(
[Id] int PRIMARY KEY IDENTITY 91,1 NOT NULL,
[Wachtwoord] varchar(50) NOT NULL,
[Rechten] varchar(100) NOT NULL,
[Gebruikersnaam] varchar(30) NOT NULL,
CONSTRAINT idx_unique_Gebruikersnaam UNIQUE(Gebruikersnaam) --Here
)
You have created an unique constraint, that is what it is called.
It is however always better to name your indexes and constraints, also the primary key you can give a name. Look at below examples.
You can create an unique index for an existing table like this
CREATE UNIQUE NONCLUSTERED INDEX idx_Gebruikersnaam
ON dbo.Medewerker(Gebruikersnaam)
in the table create it looks like this
Create table [dbo].[Medewerker]
(
[Id] int IDENTITY 91,1 NOT NULL,
[Wachtwoord] varchar(50) NOT NULL,
[Rechten] varchar(100) NOT NULL,
[Gebruikersnaam] varchar(30) NOT NULL,
constraint PK_MedewerkerId primary key (Id),
constraint idx_Gebruikersnaam unique (Gebruikersnaam)
)
Also I would use nvarchar in stead of varchar.
