Reverse Engineering ADTs in SQL Server 2000 - Part 3

Foreign key constraint.

In this article we are going to see how to change ADT that is linked to columns defined as Primary and Foreign Keys. Run script 'Create two tables with PK, FK and ADT' to create two tables - dbo.tblDepartment and dbo.tblTestEmployee with Primary Key Constraints, Foreign Key Constraint and link ADT to column DepartmentId.

You can view the previous articles below:

• Part 1
• Part 2

We can see that ADT adt_IntId is linked to column DepartmentId of parent table dbo.tblDepartment and to column DepartmentId of the child table dbo.tblTestEmployee:

select *
from INFORMATION_SCHEMA.COLUMN_DOMAIN_USAGE
where Table_Name in ('tblDepartment', 'tblTestEmployee')

The data type of ADT adt_IntId is integer.

select data_type
from INFORMATION_SCHEMA.DOMAINS
where Domain_Name = 'adt_IntId'

Now, we have a urgent request to change data type of adt_IntId from int to bigint. We know that we will have simular requests coming often and we decide to write a procedure that will do this task automatically, so we should not spend time on analyzing new coming requests.

Here is the plan:

1. Generate sql statements for create and drop Primary and Foreign Keys Constraints that are tied with columns controled by ADT and save source code
2. drop all table constraints identified in step 1
3. link new ADT to selected columns
4. recreate all dropped constraints

This plan is implemented in stored procedure dbo.up_AlterADT.

Lets review some building blocks of the procedure dbo.up_AlterADT:

A. Here is how we can obtain information about Foreign Key Constraint using user defined function:

declare @objname nvarchar(776)
declare @ctype   char(2)
set @objname = 'tblTestEmployee'
set @ctype   = 'F'
select *
from dbo.ufn_helpconstraint(@objname, @ctype)

B. Here is how to generate create Foreign Key Constraint statement using the same user defined function:

declare @TableName nvarchar(776)
declare @ConstraintType   char(2)

set @TableName = 'tblTestEmployee'
set @ConstraintType   = 'F'
select 'alter table ' +  'dbo.' + @TableName + '  add constraint ' + ConstraintName 
       + ' ' + ConstraintType
       + ' (' + ConstraintKeys + ')' + ' ' + FkReferences
from dbo.ufn_helpconstraint(@TableName, @ConstraintType)

C. Here is how to generate drop Foreign Key Constraint statement:

declare @TableName nvarchar(776)
declare @ConstraintType   char(2)

set @TableName = 'tblTestEmployee'
set @ConstraintType   = 'F'
select 'alter table ' +  'dbo.' + @TableName + '  drop constraint ' + ConstraintName 
 from dbo.ufn_helpconstraint(@TableName, @ConstraintType)

D. Here is how to identify tables, primary keys and foriegn keys affected by data type change:

declare @AdtName        sysname
set @AdtName        = 'adt_IntId'

select
       TC.Constraint_Type
      ,CU.Constraint_schema
      ,CU.Constraint_Name
      ,CU.Table_Schema
      ,CU.Table_Name
      ,CU.Column_Name
from INFORMATION_SCHEMA.KEY_COLUMN_USAGE CU inner join
     INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC
     on
         CU.Constraint_Catalog = TC.Constraint_Catalog
     and CU.Constraint_Schema  = TC.Constraint_Schema
     and CU.Constraint_Name    = TC.Constraint_Name
     and CU.Table_Catalog      = TC.Table_Catalog
     and CU.Table_Schema       = TC.Table_Schema
     and CU.Table_Name         = TC.Table_Name
     and CU.Constraint_Name    = TC.Constraint_Name
     inner join INFORMATION_SCHEMA.Columns C
     on CU.Column_Name         = C.Column_Name
     and CU.Table_Catalog      = C.Table_Catalog
     and CU.Table_Schema       = C.Table_Schema
     and CU.Table_Name         = C.Table_Name
     and Domain_Name           = @AdtName

E. Here is how to check data type of selected column

SELECT
 TABLE_NAME               as TableName
 ,COLUMN_NAME              as ColumnName
 ,DATA_TYPE                as DataType
FROM INFORMATION_SCHEMA.COLUMNS
WHERE Table_Name in ( 'tblTestEmployee', 'tblDepartment')
and Column_Name = 'DepartmentId'

F. Here is how to create a new ADT with data type bigint

if exists( select * from systypes where [name] = 'adt_BigIntId')
     exec sp_droptype 'adt_BigIntId'
exec sp_addtype 
   @typename = 'adt_BigIntId'
   ,@phystype = 'Bigint'
   ,@nulltype = 'NOT NULL'
   ,@owner    = 'dbo'

G. Here is how to see table constraints:

select *
 from INFORMATION_SCHEMA.TABLE_CONSTRAINTS
 where Table_Name in ('tblDepartment', 'tblTestEmployee')

Having all mentioned building blocks I wrote a stored procedure dbo.up_AlterADT that will replace existing ADT with new specified ADT. Here is how to execute it:

declare @AdtName sysname
set @AdtName        = 'adt_IntId'
declare @NewAdtName sysname
set @NewAdtName     = 'adt_BigIntId'
exec dbo.up_AlterADT @AdtName, @NewAdtName

Here is how to check the results:

SELECT
TABLE_NAME               as TableName
,COLUMN_NAME              as ColumnName
,DATA_TYPE                as DataType
FROM INFORMATION_SCHEMA.COLUMNS
WHERE Table_Name in ( 'tblTestEmployee', 'tblDepartment')
and Column_Name = 'DepartmentId'

Here are additional two test cases to review:

• Create self reference table with PK, FK and ADT.txt
• Create star schema with PK, FK and ADT.txt
• change ADT data type using stored procedure dbo.up_AlterADT.txt

Credits:
my wife, my kids, my teacher Ilya Petrenko
my coworkers from Viatech Inc.
sqlservercentral Forums

Links for reference:

• Creating and Modifying FOREIGN KEY Constraints
• Foreign Key Constraints
• Creating and Modifying UNIQUE Constraints