Database systems design implementation and management
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Database Systems: Design, Implementation, and Management. Chapter 7 Introduction to Structured Query Language (SQL). Data Definition Language (DDL) and Data Manipulation Language (DML). Data Definition Language (DDL) defines the structure of the database

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Database Systems: Design, Implementation, and Management

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Database Systems: Design, Implementation, and Management

Chapter 7

Introduction to Structured Query Language (SQL)


Data Definition Language (DDL) andData Manipulation Language (DML)

  • Data Definition Language (DDL)defines the structure of the database

    • E.g. tables, columns, keys, indexes, etc.

  • Data Manipulation Language (DML)manipulates the actual data contents

    • E.g. adding, modifying and deleting data

  • Understanding the difference between these two types of SQL commands will help you master SQL


Create, Read, Edit/Update, Delete (CRED/CRUD): Four major kinds of database operations

  • Create

    • DDL: CREATE tables and other structures

    • DML: INSERT data into tables

  • Read

    • DDL: SELECT (system catalogue queries)

    • DML: SELECT

  • Edit/Update

    • DDL: ALTER table and other structures

    • DML: UPDATE table

  • Delete

    • DDL: DROP tables and other structures

    • DML: DELETE from table


WHERE versus HAVING

  • WHERE is used to restrict a subset of rows from a regular query result

    • Usually a SELECT query, but also UPDATE and DELETE

  • HAVING is used to restrict a subset of rows when using a GROUP BY aggregation

    • HAVING only works with GROUP BY

  • Mnemonics to not confuse the two:

    • SELECT FROM WHERE? (WHERE is the normal clause for a SELECT statement)

    • G-H (GROUP BY goes with HAVING)


Set date and number formats in Oracle

  • Some data (e.g. dates and numbers) assume that certain formats are being used

  • ALTER SESSION is used to set environment variables, including date and number formats

  • If you have problems entering dates, execute this SQL command before your other commands:

    • alter session set nls_date_format = 'dd-mm-yyyy';

  • With language and number format problems, try:

    • alter session set nls_language = English;

    • alter session set nls_territory = Canada;


Sources

  • Most of the slides are adapted from Database Systems: Design, Implementation and Management by Carlos Coronel and Steven Morris. 11th edition (2015) published by Cengage Learning. ISBN 13: 978-1-285-19614-5

  • Other sources are noted on the slides themselves


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