1. IST 220 – Intro to DB Lab 2 Specifying Criteria in SELECT Statements

2.  We have learned in Lab 1  The SELECT statement can have up to six clauses  The first two clauses SELECT and FROM are always used  The ORDER BY clause, when used, will be the last one  In this lab, we will practice the WHERE clause, which  Comes right after the FROM clause, and  Specifies criteria: only rows meet the conditions will be retrieved Basic SELECT Syntax

3. Clauses in a SELECT Statement SELECT … FROM … WHERE … … ORDER BY …

4.  Many conditions can be specified using comparison operators (see list on right)  These operators work with all 3 types of data commonly in use:  Numbers  Dates (e.g., >= means on or after a date)  Text string (based on alphabetical order) Using Comparison Operators Comparison Operators These operators take 2 operands (or expressions) in the form Expr1 Operator Expr2 For instance, VenderState = ‘IA’ InvoiceTotal <> 0

5.  We will use the Invoices table, and retrieve data from the invoice number, date, and total amount columns  Q1: Retrieve invoices with a total amount greater than $1,000  Q2: Retrieve invoices with a date before Sept 1, 2009

6.  Sometimes a query needs to use a compound condition with multiple comparisons linked with logical operators:  AND  OR  NOT  Q3: Retrieve invoices with a total amount greater than $1,000 but less than $2,500  Q4: Retrieve invoices with a total amount less than $1,000 or greater than $2,500 Using Logical Operators

7.  BETWEEN … AND …  Specifying an inclusive range with continuous values  Q5: rewrite Q3 with this pattern  IN (…, … [, …])  Specifying a list of values  IS NULL  Matching the NULL value (a special value stands for not applicable or not available) Some Useful Operators

8.  LIKE is used for matching strings  A pattern is specified instead of exact values  The following wildcard characters are often used:  %matches any string of zero or more characters  _ matches any one single character  Q8: list vendors in cities with a name starting with the letters ‘san’ The LIKE Keyword