BTM 382 Database Management

Chapter 7Introduction to Structured Query Language (SQL)

Chitu OkoliAssociate Professor in Business Technology ManagementJohn Molson School of Business, Concordia University, Montréal

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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

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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

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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)• SELECT column-list• FROM tables• WHERE conditions

– G-H (GROUP BY goes with HAVING)4

Set date and number formats in Oracle

• Some data (e.g. dates and numbers) assume that certain formats are being used; using different formats can give errors

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

• Date formats: If you have problems entering dates, execute this SQL command before all your other commands:– alter session set nls_date_format = 'dd-mm-yyyy';

• You need to customize the date format to exactly what you want

– You can also use the function: to_date( '20150301', 'YYYYMMDD' )

• Language and number formats: These commands could help:– alter session set nls_language = English;– alter session set nls_territory = Canada;– alter session set nls_date_format = 'dd-mm-yyyy';

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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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