SQL SET

5 Key excerpts on "SQL SET"

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  eBook - ePub

  Database Modeling Step by Step

  • Gavin Powell(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  This chapter shows how the relational database model is used from an application perspective. There is little point in understanding something such as relational database modeling without seeing it applied in some way, and so this chapter looks at how a database model is accessed by applications. A relational database model contains tables, where rows in tables are accessed using a computer programming language called Structured Query Language (SQL). SQL is a declarative programming language that is used to read data from tables and update data in those tables.

  A declarative programming language describes what you are coding without describing how the problem is solved, which can be difficult to understand, because declarative code requires all instructions in a single complex instruction. Other computer programming languages such as C and FORTRAN are procedural or modular and break software down into separate parts called modules; and then there is Java, which is object-oriented.

  When a database model is well designed, the creation of SQL code can be a simpler process, which also can imply that difficulties encountered in coding of SQL queries can often indicate database model design flaws, or just too much granularity in a data model.

  This chapter covers:

  •  What SQL is •  The origins of SQL •  Different types of queries •  Changing data in tables •  Changing table structure

  4.1    What is SQL?

  SQL is a declarative computer programming language used for accessing row and column values in relational database tables:

  •  SQL is structured in the sense that it is used to access structured data from tables in a relational database. •  Use of the word “language” implies a computer programming language that has specific syntax for performing specific tasks.

  •  SQL is a declarative language consisting of single commands where the database itself does a lot of the work in deciding how to get that information. In other words, SQL tells the database what it wants, and the database does some of the logical assessment, because logic is built into a relational database using keys and relationships between tables. A procedural language, on the other hand, contains blocks of commands, where those blocks of commands are sequences of distinct steps, typically where each successive step is dependent on the result of the previous step (command) in the sequence.

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  eBook - PDF

  Developing Windows-Based and Web-Enabled Information Systems

  • Nong Ye, Teresa Wu(Authors)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  151 8 Structured Query Language Structured query language (SQL) is the most influential query language of relational data-bases. This chapter first reviews the background of SQL followed by a brief discussion on Backus–Naur form (BNF) and extended BNF (EBNF), a main notation technique used in illustrating SQL syntax. The basic SQL statements, including CREATE, UPDATE, DELETE, and QUERY data, are then explained with examples. 8.1 Introduction to SQL SQL was initially developed by IBM as a part of the System R project in the early 1970s and was named structured English query language (SEQUEL). Later, it evolved to today’s acronym: SQL. In 1986, the American National Standards Institute first pub-lished the SQL standard, called “SQL-86,” followed by the International Organization for Standardization (ISO) in 1987. Since then, SQL has been enhanced several times. The first major revision was released in 1992, known as “SQL2” or “SQL-92,” which greatly enhanced the standard specification. The SQL syntax discussed in this chapter follows the SQL2 standard. SQL3 was released with support for object-oriented data manage-ment in 1999. In 2003, extensible markup language (XML)-related features were first introduced into SQL, resulted into version SQL-2003. As of today, there are seven revi-sions, and the most recent one is SQL-2011 (ISO 9075:2011), which was formally adopted in December 2011. According to the SQL standard, SQL is composed of five main languages: • Data definition language (DDL) . DDL is used to create and modify the relation sche-mas within a database. Example commands are the CREATE, ALTER, and DROP statements. • Data manipulation language (DML) . DML is used to retrieve, store, modify, delete, insert, and update data in the database. Examples of this are the SELECT, UPDATE, and INSERT statements. • Data control language (DCL) . DCL is used to create roles, permissions, and referen-tial integrity constraints for a database.

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  eBook - PDF

  Understanding Databases

  Concepts and Practice

  • Suzanne W. Dietrich(Author)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  6 SQL: Beyond the Query Language LEARNING OBJECTIVES • To define a relational database schema in SQL satisfying the constraints of the design • To learn how to manipulate data using insert, update, and delete • To understand fundamental data security using privileges Although SQL is short for Structured Query Language, the SQL standard has evolved to include much more than just the query language. There is a data definition language for defining tables and associated constraints on the table and its attributes, including referential integrity. There is also a data manipulation language for inserting, updating, and deleting tuples from tables. In addi- tion, there are language components for defining data access privileges. This chapter highlights these features of a relational database. It is important to note that every database product is an approximation to the SQL standard. When you use a particular database product, it is important to look up the specific syntax it supports. 6.1 Data Definition Chapter 1 introduced the relational data model as a collection of relations. A relation’s schema refers to its description, indicating the attributes in the relation. A visual schema of the database includes the tables with their attributes along with yellow gold keys to indicate primary keys and orange keys to denote foreign keys linked to their associated primary keys, illustrating the referential integrity relationship between the tables. Textually, a summary syntax for a relational schema provides the table name with a list of its attributes enclosed in parentheses, underlining the attributes that form the primary key of the table. The SQL DDL specifies the syntax to create, drop, and alter tables. The SQL standard provides a sublanguage for defining a database, called a data definition lan- guage (DDL). There is a create table statement to define the table attributes with the associated types and constraints, along with any constraints that apply at the table level.

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  eBook - PDF

  Fundamentals of Database Management Systems

  • Mark L. Gillenson(Author)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  Data definition, which is operationalized with a data definition language (DDL), involves instructing the DBMS software on what tables will be in the database, what attributes will be in the tables, which attributes will be indexed, and so forth. Data manipulation refers to the four basic operations that can and must be performed on data stored in any DBMS (or in any other data storage arrangement, for that matter): data retrieval, data update, insertion of new records, and deletion of existing records. Data manipulation requires a special language with which users can communicate data manipulation commands to the DBMS. Indeed, as a class, these are known as data manipulation languages (DMLs). A standard language for data management in relational databases, known as Structured Query Language or SQL, was developed in the early 1980s. SQL incorporates both DDL and DML features. It was derived from an early IBM research project in relational databases called ‘‘System R.’’ SQL has long since been declared a standard by the American National Standards Institute (ANSI) and by the International Standards Organization (ISO). Indeed, several versions of the standards have been issued over the years. Using the standards, many manufacturers have produced versions of SQL that are all quite similar, at least at the level at which we will look at SQL in this book. These SQL versions are found in such mainstream DBMSs as DB2, Oracle, MS Access, Informix, and others. SQL in its various imple- mentations is used very heavily in practice today by companies and organizations of every description, Advance Auto Parts being one of countless examples. SQL is a comprehensive database management language. The most interesting aspect of SQL and the aspect that we want to explore in this chapter is its rich data retrieval capability.

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  eBook - ePub

  RDBMS In-Depth

  Mastering SQL and PL/SQL Concepts, Database Design, ACID Transactions, and Practice Real Implementation of RDBM (English Edition)

  • Dr. Madhavi Vaidya(Author)
  • 2021(Publication Date)
  • BPB Publications

    (Publisher)

  HAPTER 3

  Relational Query Languages

  Introduction

  This chapter introduces the readers to the Structured Query Language or SEQUEL. Structured Query Language is a set of commands, which is used for interacting with relational databases. SQL is used for a vast range of purposes, including data warehousing, e-commerce, and many more applications as backend.

  SQL is a query language that is used to retrieve and send information, and organize information in a database. SQL is widely used in business, and in other types of database administration. It allows to write various types of queries like pattern matching or using the logical or relational operators. Finally, towards the end of the chapter we will learn the data dictionaries in SQL, and how to create the constraints and to name them.

  Structure

  • Introduction to SQL
  • SQL datatypes
  • Components of SQL
  • Relational and Logical operators
  • Range operators (In, Between, Like, NULL Predicate)
  • Clauses (Distinct, where)
  • Constraints
  • Implementation of constraints in SQL
  • Integrity constraints
  • Referential integrity constraints
  • Business constraints
  • Understanding data dictionary

  Objectives

  After studying this unit, you should be able to:

  • Understand SEQUEL or SQL, and its importance
  • Know the various datatypes used in SQL
  • Find and execute various operators
  • Understand the rage operators and various clauses
  • Know the use of various types of constraints and their role in SQL
  • Understand the concept of data dictionary

  In the last chapter, we were introduced to the various operators and their use in RDBMS. In addition to it, we learnt an important concept of ER model and the need of such design approach for database designing.

  Finally, we understood what is normalization. We will learn the various forms of normalization in later chapters. This chapter is focused on learning the SEQUEL or SQL, which is very important to understand backend and the usage of SQL queries.

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