Please help explain create table syntax and reason for each line

Tom Knowlton
Tom Knowlton used Ask the Experts™
on
Please explain why each line of code exists in this script.

I am not a very experienced T-SQL programmer.

Thank you,

Tom





USE [PP]
GO

IF  EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N'[dbo].[FK_ProductMatrix_ProductType]') AND parent_object_id = OBJECT_ID(N'[dbo].[ProductMatrix]'))
ALTER TABLE [dbo].[ProductMatrix] DROP CONSTRAINT [FK_ProductMatrix_ProductType]
GO

IF  EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N'[dbo].[FK_ProductMatrix_Task]') AND parent_object_id = OBJECT_ID(N'[dbo].[ProductMatrix]'))
ALTER TABLE [dbo].[ProductMatrix] DROP CONSTRAINT [FK_ProductMatrix_Task]
GO

IF  EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N'[dbo].[FK_ProductMatrix_TaskWorkFlow]') AND parent_object_id = OBJECT_ID(N'[dbo].[ProductMatrix]'))
ALTER TABLE [dbo].[ProductMatrix] DROP CONSTRAINT [FK_ProductMatrix_TaskWorkFlow]
GO

IF  EXISTS (SELECT * FROM dbo.sysobjects WHERE id = OBJECT_ID(N'[DF_ProductMatrix_ProductMatrixSID]') AND type = 'D')
BEGIN
ALTER TABLE [dbo].[ProductMatrix] DROP CONSTRAINT [DF_ProductMatrix_ProductMatrixSID]
END

GO

USE [PP]
GO

/****** Object:  Table [dbo].[ProductMatrix]    Script Date: 11/16/2012 10:52:09 ******/
IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[ProductMatrix]') AND type in (N'U'))
DROP TABLE [dbo].[ProductMatrix]
GO

USE [PP]
GO

/****** Object:  Table [dbo].[ProductMatrix]    Script Date: 11/16/2012 10:52:09 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[ProductMatrix](
	[ProductMatrixID] [int] IDENTITY(1,1) NOT NULL,
	[ProductMatrixSID] [int] NOT NULL,
	[TaskWorkFlowID] [int] NULL,
	[TaskWorkFlowSID] [int] NULL,
	[IDTemplate] [int] NULL,
	[TaskID] [int] NULL,
	[NewProductID] [int] NULL,
 CONSTRAINT [PK_ProductMatrix] PRIMARY KEY CLUSTERED 
(
	[ProductMatrixID] ASC,
	[ProductMatrixSID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON, FILLFACTOR = 85) ON [PRIMARY]
) ON [PRIMARY]

GO

ALTER TABLE [dbo].[ProductMatrix]  WITH CHECK ADD  CONSTRAINT [FK_ProductMatrix_ProductType] FOREIGN KEY([NewProductID])
REFERENCES [dbo].[ProductType] ([ProductTypeID])
GO

ALTER TABLE [dbo].[ProductMatrix] CHECK CONSTRAINT [FK_ProductMatrix_ProductType]
GO

ALTER TABLE [dbo].[ProductMatrix]  WITH CHECK ADD  CONSTRAINT [FK_ProductMatrix_Task] FOREIGN KEY([TaskID])
REFERENCES [dbo].[Task] ([TaskID])
GO

ALTER TABLE [dbo].[ProductMatrix] CHECK CONSTRAINT [FK_ProductMatrix_Task]
GO

ALTER TABLE [dbo].[ProductMatrix]  WITH CHECK ADD  CONSTRAINT [FK_ProductMatrix_TaskWorkFlow] FOREIGN KEY([TaskWorkFlowID], [TaskWorkFlowSID])
REFERENCES [dbo].[TaskWorkFlow] ([TaskWorkFlowID], [TaskWorkFlowSID])
GO

ALTER TABLE [dbo].[ProductMatrix] CHECK CONSTRAINT [FK_ProductMatrix_TaskWorkFlow]
GO

ALTER TABLE [dbo].[ProductMatrix] ADD  CONSTRAINT [DF_ProductMatrix_ProductMatrixSID]  DEFAULT (right(@@servername,(1))) FOR [ProductMatrixSID]
GO


USE [pp]
GO

ALTER TABLE [dbo].ProductMatrix ADD  CONSTRAINT [UK_ProductMatrix_All] UNIQUE NONCLUSTERED 
(
	[ProductMatrixID] ,
	[ProductMatrixSID] ,
	[TaskWorkFlowID] ,
	[TaskWorkFlowSID] ,
	[IDTemplate],
	[TaskID] ,
	[NewProductID]
)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, FILLFACTOR = 85) ON [PRIMARY]
GO

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--Lines 4-20 are looking for the existence of Foreign Key constraints and dropping them if they exists. The table cannot be dropped as long as these constraints are in place

--Lines 29-32 are checking for the existence of the current table and dropping it if it is there

--the rest of the lines are creating the table with the necessary foreign key constraints that were dropped earlier

It is generally good practice to check for the existence of an object before dropping it so that the stored procedure doesn't error if it is not there. Dropping the objects avoids errors generated upon the creation in the second half of the procedure.
Tom KnowltonWeb developer

Author

Commented:
B - E - A utiful  !!!

: )

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