Copyright © 2005 Ed Lance Fundamentals of Relational Database Design By Ed Lance

Copyright © 2005 Ed Lance About Me Independent Database Consultant Worked with Access since 1.0 Many years designing, developing, tuning, and developing with databases. Code with.Net platform

Copyright © 2005 Ed Lance What’s this about relationships? Relational Database is a database system that organizes data according to (more or less) the rules of relational set theory. (Codd) In a relational database, we break up data into multiple tables. These tables have ‘pointers’ (keys) in the data that relate rows in one table to rows in another. This allows us to have multiple dimensions in our data without going insane.

Copyright © 2005 Ed Lance Why do I care? Relational Database Design is important because… –It allows us to organize our data in a way that doesn’t limit the user. –It allows us to model very complex data with relative ease. –It eliminates duplicate data that is hard to maintain. –It provides us a way to search and retrieve data with an easy language and gets us out of having to write all our own data handling code.

Copyright © 2005 Ed Lance The Penalties for Not Doing It Poor database performance Can’t write queries to get data the way you want it. Lots of extra work (code) to get reports they way you want. Always doing kludges to get around the design. When the customer wants to add one more of something, it’s a design change (“I need six phone numbers instead of five.”) Updating data is a nightmare

Copyright © 2005 Ed Lance Basic Concepts KeysIndexesRelationships Normal Forms

Copyright © 2005 Ed Lance Primary Keys We need to be able to uniquely identify rows in a table. Natural key – Use one or more columns together that aren’t repeated. Identity – or Autonumber, a unique number for each row, managed by the system. PK’s help us connect data in other tables to rows in the current table.

Copyright © 2005 Ed Lance Indexes An index is a data structure used by a database engine to make searches faster. Data is generally stored in the order it was input. We want to be able to filter and order by any column (or set of columns). Indexes are defined by you, but maintained by the engine. You can index one column or a set of columns.

Copyright © 2005 Ed Lance Indexes Deciding which columns to create indexes for is a matter of judgment and skill. An index can have a huge impact (usually good) on performance of queries. Too many indexes can bog down database when modifying data. Indexes do take space on disk.

Copyright © 2005 Ed Lance Relationships We use columns in tables to contain pointers to rows in other tables. By using primary key columns, we can uniquely identify rows in a table. Then by using the value of the primary key in other tables, we can tie the tables together. Columns that contain key values from another table are called foreign keys.

Copyright © 2005 Ed Lance Relationships In order for this to work, we must be careful that we don’t end up with foreign keys that point to rows that don’t exist. This is called Referential Integrity Most database engines (inc. Access, SQL Server) can enforce this for you.

Copyright © 2005 Ed Lance Relationship Types 1 – 1 –If two tables really represent the same set of items. In other words they could be merged into one table. 1 – Many –Items in one table are related to one or more items in another table. (One library has many books.) Many – Many –Items in one table are related to one or more items in another table, but the relationship exists the other way as well. (One doctor has many patients, but each patient may have more than one doctor)

Copyright © 2005 Ed Lance Relationships Finding these relationships in your customer’s data and designing tables to correctly model them is the art of relational database design. Look for repetition in existing data. Look for ‘add-on’ fields that are used to add similar items (PhoneNumber1, PhoneNumber2)

Copyright © 2005 Ed Lance Tips for Designing Think of tables as entities (nouns). –Books, products, people, events, orders Think of relationships as verbs. –Books have authors. –Products have suppliers –Orders have order details (the set of items being ordered) Test phrases for relationship types –Suppliers have many products, but each product has only one supplier. (one-to-many)

Copyright © 2005 Ed Lance What is Normal? The process of organizing relational data can be called Normalization. Codd (and follow on people) defined criteria for increasing levels of normalization in data. In the practical world we care about the first three.

Copyright © 2005 Ed Lance Normal Forms 1NF – First Normal Form –No duplicate data in columns. This means we have to break up our data into relational tables, and establish key values. NameAddressPhone1Phone2 TitleAuthorISBN.... Codd, Lance

Copyright © 2005 Ed Lance Normal Forms NameAddressPhone1Phone2 Ed NamesIDNameAddress1Ed1234NamesIDPhoneNumber

Copyright © 2005 Ed Lance Normal Forms TitleAuthorISBN.... RDBMS Codd, Lance PubsIDName1Codd 1LancePubIDTitleISBN1RDBMS

Copyright © 2005 Ed Lance Normal Forms 2NF – Second Normal Form –Be in 1NF. –All columns must be dependent on the whole primary key, not just one part of it. Not an issue if you use Autonumber keys. Part_No (PK) Supplier_Name (PK) Price Supplier Address

Copyright © 2005 Ed Lance Normal Forms 3NF – Third Normal Form –Be in 2NF –Non-key columns should not have dependencies on each other. Part_No (PK) Mfgr. Name Mfgr. Address …

Copyright © 2005 Ed Lance Questions? The End