Question

In previous versions of Visual studio there was a way to build DB using diagrams.

In 2012 they took out that possibility.

I need to create script which creates table for category tree.

    CREATE TABLE [dbo].[Categories]
(
    [Id] INT NOT NULL PRIMARY KEY IDENTITY, 
    [Name] NVARCHAR(50) NOT NULL, 
    [ParentId] INT NOT NULL DEFAULT 0, 
    [FK_Parent] int FOREIGN KEY ([ParentId]) REFERENCES [Categories]([Id]) NOT NULL
)

If I create table like this, I cannot add top level records.

Answer 1

Define top-level records as having a NULL FK_Parent. Just change your definition to allow nulls.

CREATE TABLE [dbo].[Categories]
(
    [Id] INT NOT NULL PRIMARY KEY IDENTITY, 
    [Name] NVARCHAR(50) NOT NULL, 
    [ParentId] INT NOT NULL ,
    ---llow NULL FK_Parent for top-level
    CONSTRAINT [FK_Parent] FOREIGN KEY ([ParentId]) REFERENCES [Categories]([Id])
)