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SQL (Standard Query Language) Yong Choi School of Business CSU, Bakersfield Study Objectives • Understand the basic commands and functions of SQL • Learn how to use SQL to query a database to extract useful information • Practice SQL 2 Introduction to SQL • Standard Query Language (SQL) is a computer language for the relational database model. • SQL is a nonprocedural language (click here for the example). So, it is much easier to use. – what is to be done without having to worry about how it's to be done. • Procedural language (click here for the example) – Must be programmed correctly and compiled – Java, C++, and Pascal. • SQL is relatively easy to learn – SQL commands set has a basic vocabulary of less than 100 words. Go To Next Topic 3 Back SQL Example SELECT ID, L_Name, F_Name, Salary, Dept_No FROM Employee; ID L_Name F_Name Salary Dept_No --------- ---------- ---------- ---------- ------------------------------------------------------------------------1 Kim John 1000 100 2 Johnson Steve 1200 100 3 Jonson Paul 1100 200 4 Lee Jim 1100 200 5 Basinger Jon 1300 6 Stone Sharon 1000 6 rows selected. 4 Back JAVA Example public class JavaProgramming { public static void main ( String[] args ) { long payAmount; payAmount = 123; System.out.println("The variable contains: " + payAmount ); } } • Output: The Variable contains 123. 5 Basic SQL Commands • Followings are the most frequently used commands – Use always • SELECT <field list> • FROM <table list> – Use when conditions must be specified • WHERE <condition> • HAVING <group condition> • ORDER BY <sorting field> • GROUP BY < grouping records> 6 The SELECT and FROM Statement • Need both commands almost always….. – The SELECT statement is used to select data from a table. – The FROM statement is used to select tables. • Syntax: – SELECT column_name(s) – FROM table_name • To select all columns (fields) from a table, use * symbol instead of column names: – SELECT * – FROM table_name 7 The WHERE Statement • To conditionally select data from a table, a WHERE clause can be added to the SELECT statement. • Syntax: – SELECT column – FROM table – WHERE column operator value • See next slide for various operators 8 SQL Comparison Operators FOR WHERE clause AND logical operator OR logical operator NOT Warehouse =‘3’ LIKE: LIKE ‘a*’, LIKE ‘*s’, Like ‘*Oxford*’ BETWEEN 45000 AND 78000 9 Semicolon after SQL Statements? • Semicolon is the standard way to a block of SQL statement in database systems. So, you must use a semicolon at the end of a block of SQL statement. – Access SQL commands are not case sensitive but try to follow exact names for better readability. • Download SQL data file form the class web site. – SQL_300.mdb 10 Customer CustomerNum CustomerName Street City State Zip Balance 148 Al's Appliance and Sport 2837 Greenway Fillmore FL 33336 $6,550 CreditLimit $7,500 RepNum 20 OrderLine OrderNum PartNum 21608 AT94 NumOrdered QuotedPrice 11 $21.95 Orders OrderNum 21608 OrderDate 10/20/2003 CustomerNum 148 Part PartNum Description AT94 Iron OnHand 50 Class Warehouse HW 3 Price $24.95 Rep RepNum LastName FirstName Street City State Zip 20 Kaiser Valerie 624 Randall Grove FL 33321 Commission $20,542.50 Rate 0.05 11 SQL Preparation • Review tables and relationships first… – Review each table in both views • Design view • Datasheet view – Recognize PK and FK information – Examine Relationships information • SQL using Access – Design view of query Select SQL View using Style button – No need to add tables (unlike QBE) 12 SQL Sample • I’d like to know the list of CustomerNum and CustomerName. – SELECT CustomerNum, CustomerName – FROM Customer; • I’d like to know the list of PartNum, Description, RepNum, and LastName – SELECT PartNum, Description, RepNum, LastName – FROM Part, Rep; 13 SQL Example 1 & 2 • Example 1: – I’d like to know a list of the Customer number, Customer name, and balance of all customers. – Save as SQL 1 • Example 2: – I’d like to know a list of the Order number, Part number, Price and Order Date. – Save as SQL 2 14 SQL Example 3 • Restriction requirements – Where command – Exact Match • Example 3: – I’d like to know customer names who are located in the city of Grove – Save as SQL 3 15 SQL Query to Find All Customers in ‘Grove’ 16 SQL Example 4 • Restriction requirements – Where command – Comparison operator • Example 4: – I’d like to know a list of the number, name, credit limit, and balance for customers with credit limits that exceed their balances. – Save as SQL 4 17 Query to find Customers with Credit Limit Exceeding Balance 18 SQL Example 5 • Restriction requirements – Where command – Compound conditions • Example 5: – List the description of all parts that are located in warehouse 3 and for which there are more than 20 units on hand. – Save as SQL 5 19 SQL Query with Compound Condition using ‘AND’ 20 SQL Example 6 • Default value of ORDER BY: ascending • Example 6: – List the number, name, and credit limit of all customers. Sort the customers by name in ascending order. – Save as SQL 6 21 SQL Query to Sort Data 22