BTM 382 Database Management Chapter 7 Introduction to Structured Query Language (SQL) Chitu Okoli Associate Professor in Business Technology Management John Molson School of Business, Concordia University, Montréal 1

Data Definition Language (DDL) and Data 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 2

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 3

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( ' ', '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'; 5

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: Database Systems: Design, Implementation and Management Other sources are noted on the slides themselves 6