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School/+2

70-229-Designing and Implementing Databases with Microsoft SQL Server 2000 Enterprise Edition

 

Before you start

This study guide provides you with information on the many different aspects of "SQL Server 2000 Database Design". Before you proceed with this subject, please read through the study material for the following and make sure you are 100% comfortable with the SQL Server architecture

  • SQL Server 7 Admin 70-028

  • SQL Server 7 Database Design 70-029

The reason you need to be familiar with SQL 7 is that the new version has many things similar to the version 7. Especially for the database design concepts, they are about the same.

 

Version 7 and Version 2000 have too many things in common. In fact, experience on 70-028 and 70-029 will be extremely helpful. This study guide will have its focus on the new features of SQL Server 2000.

Do NOT rely solely on this study notes for the exam. By all means read more than one book on the subject and make sure you understand the material well enough so that you could be ready for the questions. There is no quick way to succeed for this topic. Ideally you must work things out and gain experience before even trying to sign up for the exam.

 

Your Study Track for SQL Server 2000 DB Design

Make sure you are comfortable with the concept of Relational Database System. SQL Server is a relational database system. Also know about SQL Structured Query Language, which is the language you will use to control many of the database operations.

Make sure you know the basic concept of the Client Server Computing Model. The client presents and manipulates data on the desktop computer, while the server runs at the back end to store and retrieve protected data. SQL Server mostly works in a multi tier set up, but not as the front end though.

As of this writing many of the SQL Server 2000 resources are still in BETA testing stage. Due to the lack of SQL 2000 material in the market, you may want to start with those of SQL 7 first. Version 7 and Version 2000 have too many things in common. This study guide will have its focus on the new features of version 2000 of SQL Server. You should visit the following pages to get yourself familiar with the version 7 fundamentals before proceeding

Information for Version 7 of SQL Server DB Design should have covered the following identical information:

  • Developing a Logical Data Model

  • Create and alter databases

  • Create and alter database objects

  • Alter database objects to support replication

  • Troubleshoot failed object creation

  • Retrieving and Modifying Data

  • Programming Business Logic

  • Manage data manipulation

  • Tuning and Optimizing Data Access

  • Designing a Database Security Plan

  • Create and manage application roles

Know XML, as SQL Server 2000 has integrated into it the support of XML. Short for Extensible Markup Language, XML is a specification developed by the W3C. Being the pared-down version of SGML, it is designed especially to allow designers to create their own customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations.

Data Types

SQL Server 2000 introduces the 64-bit integer (bigint), variant (sql_variant), and table data types. The bigint data type is an integer that supports data from -9,223,372,036,854,775,808 through 9,223,372,036,854,775,807 with a storage size of 8 bytes. Note that functions will return bigint only if the parameter expression is a bigint data type, and that SQL Server will not automatically promote other integer data types to bigint. Sql_variant data type does not store values of text, ntext, image, timestamp, and sql_ variant. It allows a single column to store data values of different types.

To support the new bigint data type, we have two new built-in functions that return integer value of type bigint:

BIG_COUNT

ROWCOUNT_ BIG

To work with a sql_variant data type, you should always cast the variant with the CAST operator. For example:

SET @xyz_chr = CAST(@xyz_var AS VARCHAR(12))

SQL_VARIANT_PROPERTY is a function for returning the base data type and other information about a sql_variant instance. The syntax:

SQL_VARIANT_PROPERTY(expression, property)

The property parameter contains the name of the sql_variant property that can take a value of BaseType, Precision, Scale, TotalBytes, Collation, or MaxLength.

An extended property has a name and a value being as a sql_variant with a size of max 7500 bytes. For operations related to the adding, updating, and dropping extended properties, the following SP can be used:

  • o sp_ setextendedproperty

  • o sp_dropextendedproperty

  • o sp_updateextendedproperty

In addition, you can use the user-defined function fn_listextendedproperty to retrieve the extended properties if needed.

Table data type is a local variable for temporarily storing a rowset. It can be used in place of temporary tables of the tempdb database. Keep in mind that table data type is managed in memory only, it provides performance benefits over other disks based alternatives. You define such a data type like this:

DECLARE @local_variable TABLE <table_definition>

Together with a user defined function that returns a table data type, you can declare an internal table variable and return that variable as the return value. We refer this as rowset functions. This is an attractive alternative to views, given the fact that views are limited to a single select statement, while user-defined functions can contain multiple statements in views, as they can be included in the FROM clause of a SQL statement.

 

User-defined Functions and Triggers

User-defined functions are similar to stored procedures. They accept zero or more input parameters, and can return a scalar data type such as int, decimal, varchar, or sql_variant as well as the table data type. However, you must specify the RETURNS value and to terminate with the RETURN statement.

To have a user-defined function returns a scalar data type, you need to define the return type and specify the value in the return statement:

CREATE FUNCTION dave.MyProductsTable ()

RETURNS TABLE

AS

RETURN SELECT TOP 5

ProductName AS MyProducts, UnitPrice

FROM Products

ORDER BY Products.UnitPrice

 

When the return type is a local table variable, this allows you to use the local table variable for inserts and other operations prior to the return.

A special type of table exists that returns a user-defined function (in-line function). It has a return type of table without the table definition. It actually returns the resultset of a single select statement from which the table definition is derived.

One reason of using function over stored procedure is that it allows you to include the function in the select statement:

SELECT Products.*, Manu.*

FROM MyProductsTable() AS MyProducts

INNER JOIN …

 

You need to understand the determinism of a function, as all functions are either deterministic or nondeterministic. Deterministic functions always return the same result for a given set of parameters, while nondeterministic functions do not.

SCOPE_IDENTITY is a function to be used for the @@IDENTITY global variable to return the last value inserted into an identity column that has the same scope. IDENT_CURRENT is a function to be used for the @@IDENTITY global variable to return the last identity value generated for a specified table in any session and any scope.

Triggers are special stored procedures for executing instructions automatically when there is an update, insert, or delete statement raised against a table. You can find two new trigger types in SQL Server 2000, the AFTER trigger and the INSTEAD OF trigger. AFTER is for table use only. For an AFTER trigger to fire, the statement must complete without an error. You may specify multiple AFTER triggers for each triggering action, and you may specify the order of trigger execution using sp_settriggerorder. Note that all other AFTER triggers will fire in undefined order. In contrast, INSTEAD OF triggers can be specified on both tables and views.

 

Integrity Constraints

There are many different types of integrity. Domain Integrity refers to the requirement that data values in each column must be valid. To enforce, use Primary and Foreign Keys, Default definitions and Check constraints. With Entity Integrity, each row in a given table must be unique in the entity. To enforce, you use primary key. With Referential Integrity, relationships between tables are maintained through Primary Key and Foreign Key. In SQL Server 2000, this referential integrity concept has been extended to support cascading delete and update operations.

With the NO ACTION constraint, you can prevent data on a referenced table from being deleted or updated if corresponding records exist on the referring table. You can also prevent data on the referring table from being inserted or updated if no corresponding entry exists on the referenced table.

CONSTRAINT FK_myOrder_Details FOREIGN KEY

(OrderID) REFERENCES dbo.myOrders(OrderID)

ON UPDATE NO ACTION

ON DELETE NO ACTION,


You may also allow update and delete operations to be cascaded from the referenced table to the referred table. For example, if you change an exam code, it may make more sense to cascade this new code to all the related exam detail records. You do this with:

ON UPDATE CASCADE

 

Performance

There are mainly two kinds of database systems: OLTP and DSS. With OLTP you want to make sure update is fast and table structure is optimized. You tend to normalize the tables to avoid data redundancy. We classify data as redundant when data is irrelevant; data has duplicates; or data is basically extracted from another column of data. Note that with DSS you need fast retrieval speed, and redundant data is unavoidable.

In a First Normal Form, no table has columns that define similar attributes and no column contains multiple values in a single row. In a Second Normal Form, each column that is not part of the primary key should depend on all columns that make a composite Primary key and not only depend on a subset of the composite Primary key. In a Third Normal Form, columns that are not covered by the Primary Key should not depend on each other. You may not want to go to Fourth Normal Form and Fifth Normal Form, as they may involve too many complex joins which are costly to process.

The more the joins involved in a query, the more workload a processor has to handle. Inner Joins uses a comparison operator to match rows from two columns based on the values in the common columns to return rows that match. In contrast, Outer Joins returns all rows from at least one of the tables or views specified in the From clause. With Left Outer Joins, you may return all rows from the left table regardless, and that the right table will return NULL where there is no match. Right Outer Join is the other way around. Full Outer Joins returns all rows from both tables, and that NULL values will fill the non-matched fields. With Cross Joins, all rows in the left table are matched with all rows in the right table to produce a Cartesian product which is most likely meaningless. Sometimes you may prefer to use the UNION clause to combine the result sets from multiple SELECT statements into one result set if the result sets contain the same number of columns with compatible data types.

When we talk about UNION, we should also know that SQL Server 2000 supports updateable UNION views over local or remote linked servers, known as distributed partitioned views. This allows servers to cooperate to provide a single view of partitioned data and provide unlimited scalability. To define distributed partitioned views, you need to first create an image of the database on each of the participating servers, then define the member tables, then define each member server as linked server, and finally define the distributed partitioned views in all of the member databases. This type of partitioning is known as horizontal partitioning.

Generally, for OLTP, disk I/O is always the bottleneck. To optimize I/O performance, you should place tables and indexes across as many different physical disks as possible, and placing the transaction log on its own disk. Also, for tables that are likely to participate in joins, you should place them on different disks so that they can be scanned in parallel.

Know when to use clustered index and when to use non-clustered index. Since clustered index actually rearrange the actual order of the records, there can be only one per table. Generally, clustered index should be kept as narrow as possible to reduce disk space consumption and reduce I/O burden caused by data modification in the table. In contrast, Non-clustered indexes use the clustered index keys as pointers to data. You should create clustered index on the Primary key column and create non-clustered indexes on columns often used in WHERE clauses. Always use the column that has more unique values first in a composite index.

SQL Server Query Analyzer is a GUI tool tightly integrated with the Index Tuning Wizard and SQL Server Profiler that enables you to write queries, execute multiple queries simultaneously, view results, analyze the query plan, and receive assistance to improve the query performance. Database Maintenance Plan Wizard helps setting up the core maintenance tasks necessary to ensure your database performs well. Note that maintenance activates can also include back up, check for integrity and consistency…etc.

New in SQL Server 2000 is indexed view. In SQL Server 2000, a view that has a unique clustered index is referred to as an indexed view. You may actually create a unique clustered index as well as non-clustered indexes on a view to improve data access performance on complex queries. However, keep in mind that not all queries will benefit from indexed views. Most importantly, if the indexed views are not used, there is no benefit.

You should consider using indexed view in schema that involves any subset of tables referenced in the query, any subset of the conditions in the query for that subset of tables, grouping columns or aggregate functions.

Decision support queries usually reference large numbers of rows and aggregate large amounts of information into concise aggregates. By using indexed view you will force the view's resultset to be stored in the database, leading to substantially better response times.

With the NOEXPAND option you can force the query optimizer to treat the view like an ordinary table with a clustered index. Or you can explicitly exclude indexed views from consideration by using the EXPAND VIEWS option with the query. The SCHEMABINDING option is used to prevent the base referenced tables from being changed without view adjustment. For the best result, indexes on tables and indexed views should be designed concurrently to avoid redundant recommendations that incur high storage and maintenance overhead. Also, when designing the indexed view, you should design them to be used by multiple queries and to keep the index as small as possible by using the fewest number of columns and bytes. Sometimes multiple smaller indexed views are preferable than a single big one.

You may use Index Tuning Wizard for creating indexed view, as it will make recommendation for you. For maintenance, SQL Server automatically take care of it. However, if the indexed view references several tables, updating any of them may require updating the indexed view, which is expensive relatively. You need to take this into account before considering the use of indexed view, if the view will reference multiple sources.

To define an index on a view, use the create index statement as follow:

CREATE UNIQUE CLUSTERED INDEX myindex ON OrderTotals (OrderID)

Nonclustered indexes are supported only on view with previously defined unique clustered index. Indexes defined on computed columns are allowed if the expression defined for the column only references columns from the table containing the computed column and is deterministic, meaning calculated values do not change subsequent invocations. Using indexes on computed columns is recommended when you are trying to create covering indexes. For views using the GROUP BY aggregation, the COUNT_ BIG(*) statement is mandatory. In addition, all grouping columns must appear in the view's select list.

Keep in mind that index cannot be created on a computed column if the column expression references nondeterministic functions. Also, clustered index cannot be created on a view if the view references nondeterministic functions.

 

Collations

With SQL Server 7.0, during install you must specify a default code page and sort order. All databases will then be locked into that particular code page and sort order. In SQL Server 2000, collation acts as a collection of the sort order for Unicode data types, the sort order for non-Unicode character data types, and the code page that is used to store non-Unicode character data types. You can specify collations at the database or column level, in addition to the default collation specified during installation. In addition to support collations at design time, you may specify collations for individual statements to create queries on tables supporting multilingual data specific to the language of the data.

Take a look at this example code fragment for column level collation:

CREATE TABLE myBody (

myName NVARCHAR(128) COLLATE SQL_Latin1_General_CP1_CI_AI,

myType VARCHAR(10),

myLang VARCHAR(10),

)

Take a look at this example code fragment for database level collation:

CREATE DATABASE myBody

COLLATE SQL_Latin1_General_CP1_CI_AI

 

XML

In terms of XML Data Retrieval, results of SELECT statements can be returned as XML document fragments through using the FOR XML clause:

FOR XML {mode} [,XMLDATA][, ELEMENTS][, BINARY Base64]

With RAW mode you transform each row in the SQL query into an XML element with the generic row identifier. With AUTO mode you can return query results in a nested XML tree. Within AUTO mode you can specify the ELEMENTS option to have columns returned as sub-elements. The option BINARY Base64 allows you to have binary data to be returned in base64 encoding. The XMLDATA option you can specify that XML-Data schema information should also be returned together.

With EXPLICIT mode you can specify the shape of the XML tree for manually ensuring the generated XML structure. The EXPLICIT mode query will produce a universal table with information about the resulting XML tree, and the table will be vertically partitioned into groups to transform into XML elements. The Tag column will store the tag number of the current element. The parent column will store the tag number of the parent. You use these metadata tags together to describe a parent and child hierarchy in the XML tree.

OpenXML is a rowset function used to expose data from the XML document as a relational rowset. You may use it as a table reference and allow yourself to use the data in XML documents for inserts or updates into database tables. However, to use it you must first create an internal instance of an XML document with sp_xml_preparedocument. Remove it with sp_xml_removedocument to free up memory once your job is done.

When we talk about XML you may wonder about the web integration aspect of SQL Server 2000. SQL Server always act as the backend in the scenario. You may use the variant datatype for internet application that collects information from users. When someone submit a value via a form, instead of saving the form value as character together with all associated metadata, you can simply save the value as a sql_variant with proper casting in place.

 

SQL Structure

For the SQL language, make sure you fully understand how SQL is used in TSQL context. With the Where clause, aggregate functions cannot be used. Without a Where clause, a tablescan will occur that degrade performance. With the Group clause, all columns in the Select list must occur in the Group clause with NO aliase. With the Having clause, all columns must be listed in the group by clause or be used in aggregate functions. With the Order By clause, all columns in the Compute by clause must appear in the order by clause. With the Compute By clause all columns presented in the compute by clause must be listed in the ORDER BY clause without aliases. The main difference between COMPUTE and GROUP BY is that GROUP BY produces a single result set, while COMPUTE produces multiple result sets.

It is important to remember the order of SQL commands after the Select clause, from clause and where clause: Group By + Having / Order by + Compute By. In the Transcender 029 exam you will see a lot of practical cases relevant to this topic. Also make sure you know how to read ER Diagram and know how to distinguish between one to one, one to many and many to many relationships. Also be sure to know what is the best column for creating primary key and foreign key.



 
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