The SELECT reserved word is part of the Data Manipulation Language (DML) defined by Codd and is used to query data from the database. Because of its popularity, there are many clauses and functions that can be used to construct a query to retrieve data. Today, I am continuing our exploration of this reserved word by reviewing queries that merge data using joins and unions. Six known join types exist in SQL Server. The definitions are based upon joining TABLE A (left) with TABLE B (right). Inner Join – Include…
Month: August 2011
Crafting Databases – Part 4
The ALTER TABLE statement is part of the Data Definition Language (DDL). The statement is used to modify a table after it has been created. Today, I would like to talk about the three integrity concerns that data modelers deal with. Integrity Concerns Entity Data Integrity – Adding primary keys to makes sure rows are unique. Referential Data Integrity – Adding foreign keys to make sure relationships are maintained. Domain Data Integrity – Creating constraints or triggers enforce the range of data values. Again, we will be working with the…
Crafting Databases – Part 3
The CREATE TABLE statement is part of the Data Definition Language (DDL). It is used to define a structure to hold rows of data or tuples if we use Relational Algebra concepts. Each table is defined by a set of fields of a certain data type and precision. Data Types can be categorized as the following. Exact numerics Approximate numerics Character strings Unicode character strings Binary strings Date and time Other data types The power of a database comes from creating user defined datatypes (UDT). Some of the benefits of…
Crafting Databases – Part 2
The CREATE LOGIN and CREATE USER statements are part of the Data Definition Language (DDL) defined by Codd. Basically, a server login has to be defined so that person can connect to the server and a user login has to be created to map the server login to a particular database. I am going to continue my talk with the BSA hypothetical business problem from Part 1. Server logins allow access at the server level which can be defined using Windows Authentication or a SQL Server Authentication. Windows Authentication assumes…
Crafting Databases – Part 1
The CREATE DATABASE SQL statement is part of the Data Definition Language (DML) defined by Codd and is used define (CREATE), modify (ALTER) or remove (DROP) databases along with there associated files. Before I talk about crafting a database, I want to classify SQL statements by four known groups. Data Definition Language (DDL) statements are SQL statements that support the definition or declaration of database objects. CREATE ALTER DROP Data Manipulation Language (DML) is a vocabulary used to add, modify, query, or remove data from a SQL Server database. SELECT…