SQL – Structured Query Language: Introduction, Evolution

SQL is a programming language that is used to communicate and manipulate databases. SQL, which stands for Structured Query Language, is a programming language that is used to communicate with and manipulate databases. In order to get the most of the mounds of data they collect, many businesses must become versed in SQL.   SQL [ [ ...]

Introduction to SQL language: Role, Features and Benefits

The SQL language and relational database systems based on it are one of the most important foundation technologies in the computer industry. Over the last two decades, SQL has grown from its first commercial use into a computer product and services market segment worth tens of billions of dollars per year, and SQL stands today [ [ ...]

A Quick Tour of SQL

Before diving into the details of SQL, it’s a good idea to develop an overall perspective on the language and how it works. This chapter contains a quick tour of SQL that illustrates its major features and functions. The goal of the quick tour is not to make you proficient in writing SQL statements; that [ [ ...]

SQL and Database Management

One of the major tasks of a computer system is to store and manage data. To handle this task, specialized computer programs known as database management systems began to appear in the late 1960s and early 1970s. A database management system, or DBMS, helped computer users to organize and structure their data and allowed the [ [ ...]

A Brief History of SQL

The history of the SQL language is intimately intertwined with the development of relational databases. Table 3-1 shows some of the milestones in its 30-year history. The relational database concept was originally developed by Dr. E.F. “Ted” Codd, an IBM researcher. In June 1970, Dr. Codd published an article entitled “A Relational Model of Data [ [ ...]

SQL Standards

One of the most important developments in the market acceptance of SQL is the emergence of SQL standards. References to “the SQL standard” usually mean the official standard adopted by the American National Standards Institute (ANSI) and the International Standards Organization (ISO). However, there are other important SQL standards, including the de facto standard for [ [ ...]

SQL and Networking

The dramatic growth of computer networking in the 1990s had a major impact on database management and gave SQL a new prominence. As networks became more common, applications that traditionally ran on a central minicomputer or mainframe moved to local area networks of desktop workstations and servers. In these networks, SQL plays a crucial role [ [ ...]

The Proliferation of SQL

As the standard for relational database access, SQL has had a major impact on all parts of the computer market. IBM has adopted SQL as a unifying database technology for its product line. SQL-based databases dominate the market for UNIX-based computer systems. In the PC market, SQL databases on server-oriented Windows operating systems are mounting [ [ ...]

Early Data Models

As database management became popular during the 1970s and 1980s, a handful of popular data models emerged. Each of these early data models had advantages and disadvantages that played key roles in the development of the relational data model. In many ways, the relational data model represented an attempt to streamline and simplify the earlier [ [ ...]

The Relational Data Model

The relational model proposed by Dr. Codd was an attempt to simplify database structure. It eliminated the explicit parent/child structures from the database, and instead represented all data in the database as simple row/column tables of data values. Figure 4-5 shows a relational version of the network order-processing database in Figure 4-4. Unfortunately, the practical [ [ ...]

Codd’s 12 Rules*

In his 1985 Computerworld article, Ted Codd presented 12 rules that a database must obey if it is to be considered truly relational. Codd’s 12 rules, shown in the following list, have since become a semiofficial definition of a relational database. The rules come out of Codd’s theoretical work on the relational model and actually [ [ ...]

SQL Basics: Statements

The main body of the SQL language consists of about 40 statements. The most important and frequently used statements are summarized in Table 5-1. Each statement requests a specific action from the DBMS, such as creating a new table, retrieving data, or inserting new data into the database. All SQL statements have the same basic [ [ ...]

SQL Basics: Table Names & Column Names

The objects in a SQL-based database are identified by assigning them unique names. Names are used in SQL statements to identify the database object on which the statement should act. The most fundamental named objects in a relational database are table names (which identify tables), column names (which identify columns), and user names (which identify [ [ ...]

SQL Basics: Data Types

The ANSI/ISO SQL standard specifies the various types of data that can be stored in a SQL-based database and manipulated by the SQL language. The original SQL1 standard specified only a minimal set of data types. The SQL2 standard expanded this list to include variable-length character strings, date and time data, bit strings, and other [ [ ...]

SQL Basics: Constants

In some SQL statements a numeric, character, or date data value must be expressed in text form. For example, in this INSERT statement, which adds a salesperson to the database: I INSERT INTO SALESREPS (EMPL_NUM, NAME, QUOTA, HIRE_DATE, SALES) VALUES (115, ‘Dennis Irving’, 175000.00,  ’21-JUN-90′, 0.00) the value for each column in the newly inserted row [ [ ...]

SQL Basics: Expressions

Expressions are used in the SQL language to calculate values that are retrieved from a database and to calculate values used in searching the database. For example, this query calculates the sales of each office as a percentage of its target:  SELECT CITY, TARGET, SALES, (SALES/TARGET) * 100 FROM OFFICES and this query lists the [ [ ...]

SQL Basics: Built-In Functions

Although the SQL1 standard doesn’t specify them, most SQL implementations include a number of useful built-in functions. These facilities often provide data type conversion facilities. For example, DB2’s built-in MONTH() and YEAR() functions take a DATE or TIMESTAMP value as their input and return an integer that is the month or year portion of the [ [ ...]

SQL Basics: Missing Data (NULL Values)

Because a database is usually a model of a real-world situation, certain pieces of data are inevitably missing, unknown, or don’t apply. In the sample database, for example, the QUOTA column in the SALESREPS table contains the sales goal for each salesperson. However, the newest salesperson has not yet been assigned a quota; this data [ [ ...]

Simple Queries in SQL: The SELECT Statement

The SELECT statement retrieves data from a database and returns it to you in the form of query results. You have already seen many examples of the SELECT statement in the quick tour presented in Chapter 2. Here are several more sample queries that retrieve information about sales offices: List the sales offices with their [ [ ...]

Simple Queries in SQL: Query Results

The result of a SQL query is always a table of data, just like the tables in the database. If you type a SELECT statement using interactive SQL, the DBMS displays the query results in tabular form on your computer screen. If a program sends a query to the DBMS using programmatic SQL, the table [ [ ...]