SQL – Part II

SQL – Part II

Yong Choi

School of Business

CSU, Bakersfield

SQL Examples – Aggregate Functions

• Example 18: Save as example 18– How many parts (count number of records) are

in item class HW? – Use of “count” command– Count all records: count(*)

Example 18SQL Query to Count Records

Example 18SELECT count(*)FROM PartWHERE Class="HW";

SQL Examples – Aggregate Functions

• Example 19: Save as example 19– Find the number of customers and the total of

their balances.– Calculate total: sum(field name)

Example 19SQL Query to Count Records and

Calculate a Total

Example 19

SELECT count(*), Sum(Balance)FROM Customer;

SQL Examples – Aggregate Functions

• Example 20: Save as example 20– Find the total number of customers and the total

of their balances. Change the column names for the number of customers and the total of their balances to CustomerCount and BalancesTotal.

– Change column name using “AS” command

Example 20SQL Query to Perform Calculations and

Rename Fields

Example 20

SELECT count(*) AS CustomerCount, Sum(Balance) AS BalanceTotal

FROM Customer;

SQL Examples – Nested Query

• A query inside another query– A inside query (sub-query) is evaluated first. – It is common to enclose sub-query in parentheses for

readability!!

• Example 21: Save as example 21– List the order number for each order from the order

line table for a part located in warehouse 3.– Think about connection between tables (OrderLine

and Part).

Example 21SQL Query with Subquery

Example 21SELECT OrderNumFROM OrderLineWHERE PartNum IN

(SELECT PartNum FROM PartWHERE Warehouse='3');

SQL Examples - Grouping

• Use GROUP BY clause– ONLY grouping, NOT sorting (usually associated

with ORDER BY clause)

• Example 22: Save as example 22– For each sales rep, list the rep number, the

number of customers assigned to each rep, and the average balance of the rep’s customers.

– Rename the count of the number of customers and the average of the balances to NumOfCustomers and AverageBalance

Example 22SQL Query to Group Records

Example 22SELECT RepNum,

Count(*) AS NumOfCustomer, Avg(Balance) AS AvgBalance

FROM CustomerGROUP BY RepNum

SQL Examples – Grouping (con’t)

• Example 23: Save as example 23– For each sales rep with fewer than four customers, list

the rep number, the number of customers assigned to the rep, and the average balance of the rep’s customers. Rename the count of the number of customers and the average of the balances to NumOfCustomers and AverageBalance.

– Use of “Having” command.

Example 23 SQL Query to Restrict Groups

Example 23

SELECT RepNum, count(*) AS NumCustomer, Avg(Balance) AS AverageBalance

FROM CustomerGROUP BY RepNumHAVING Count(*)<4;

SQL Examples – Grouping (con’t)

• Use of Where and Having clauses together– “Where” command must be stated first

• Example 23-1: Save as example 23-1– Exactly same as example 23. Except, only groups

with fewer than three records and customers with credit limit of less than $10,000 must be included.

Example 23-1SQL Query with ‘WHERE’

and ‘HAVING’ Clauses

Example 23-1

SELECT RepNum, count(*) AS NumCustomer, Avg(Balance) AS AverageBalance

FROM CustomerWHERE CreditLimit<10000GROUP BY RepNumHAVING Count(*)<3;

SQL Examples – Joining Tables

• Use of multiple tables• Example 24: Save as example 24

– List the number and name of each customer together with the number, last name, and first name of the sales rep who represents the customer.

• CustomerNum, CustomerName, RepNum, LastName, FirstName

Example 24SQL Query to Join Tables

Example 24

SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName

FROM Customer, RepWHERE Rep.RepNum=Customer.RepNum;

SQL Examples – Joining Tables (con’t)

• Use of multiple tables with a compound condition

• Example 25: Save as example 25– List the number and name of each customer

whose credit limit is $10,000 together with number, last name, and first name of the sales rep who represents the customer.

Example 25Query to Restrict Records in Join

Example 25

SELECT CustomerNum, CustomerName, Rep.RepNum, LastName, FirstName

FROM Customer, RepWHERE Rep.RepNum=Customer.RepNumAND CreditLimit=10000;

SQL Examples – Joining Tables (con’t)

• Example 26: Save as example– For every order, list the order number, order date,

customer number, and customer name. In addition, for each order line within the order, list the part number, description, number ordered, and quoted price.

– How many tables?– How many conditions?

Example 26Query to Join Multiple Tables

Example 26

SELECT Orders.OrderNum, Orderdate, Customer.CustomerNum, CustomerName, Part.PartNum, Description, NumOrdered, QuotedPrice

FROM Orders, Customer, OrderLine, PartWHERE

Customer.CustomerNum=Order.CustomerNum AND Order.OrderNum=OrderLine.OrderNum AND OrderLine.PartNum=Part.PartNum;

SQL Examples – Union

• The union of two tables is a table containing all rows that are in either the first table, the second table, or both tables. – Two tables involved in union must have same structure.

• Example 27: Save as example 27– List the number and name of all customers that

are either represented by sales rep 35 or that currently have orders on file, or both.

Example 27 SQL Query to Perform UnionRed: Currently have orders on fileBlue: Represented by sales rep 35

Green: Both

Example 27

SELECT CustomerNum, CustomerNameFROM CustomerWHERE RepNum='35'

UNION SELECT Customer.CustomerNum, CustomerNameFROM Customer, OrderWHERE Customer.CustomerNum=Order.CustomerNum;

Three Basic Functions by SQLAnd Their Basic SQL Commands

1.Data definition (last topic) through the use of CREATE

2.Data manipulation (next topic) through INSERT, UPDATE, and DELETE

3.Data querying (we are done with this) through the use of SELECT AND MANY OTHERS, which is the basis for all SQL queries.

SQL - Data Manipulation

• Possible with Access– UPDATE– INSERT– DELETE

• Possible with enterprise level DBMS– COMMIT– ROLLBACK

SQL - Data Manipulation (con’t)

• UPDATE command makes data entry corrections

UPDATE Project

SET PrjtLocat = 'Bellaire', DeptNum = 5

WHERE PrjtNum = 10;

UPDATE Employee

SET Salary = Salary * 1.1

WHERE Branch = 'Lincoln';

SQL - Data Manipulation (con’t)

• INSERT command add new data to a table

INSERT INTO Employee (SSN, LastName, FirstName)

VALUES ('Richard', 'Marini', '43433');

• DELETE command removes table row

– DELETE FROM Employee– WHERE LastName = 'Brown';

SQL - Data Manipulation (con’t)

• COMMIT command store data on the secondary memory permanently

• ROLLBACK command restores database back to previous condition if COMMIT hasn’t been used

SQL Examples - Data Manipulation

• Example 28: Save as example 28– Change the street address of customer 524 to

1445 Rivard– First, review the current street address of

customer 524 (838 Ridgeland)

Example 28

UPDATE Customer SET Street = '1445 Rivard'WHERE CustomerNum='524';

SQL Examples - Data Manipulation

• Example 29: Save as example 29– Add a new sales rep to the Rep table. Her number

is 16, her name is Sharon Rands, and her address is 826 Raymond, Altonville, FL 32543. She has not yet earned any commission, but her commission rate is 5%(0.05).

Example 29

INSERT INTO RepVALUES ('16', 'Rands', 'Shron', '826

Raymond', 'Altonville', 'FL', '32543', 0, 0.05);

SQL Examples - Data Manipulation

• Example 30: Save as example 30– Delete any row in the Orderline table in which the

part number is BV06– First, review the part number BV06

(OrderNum21617)

Example 30

DELETE *FROM OrderLineWHERE PartNum='BV06';

SQL Examples – Creating a New Table Using a Existing Table

• Example 31: save as example 31– Create a new table named SmallCust, consisting

of all fields from the Customer table and those rows in which the credit limit is less than or equal to $7,500.

SELECT INTO Name of table to createFROMWHERE

Example 31SQL Query to Create New Table

Example 31

SELECT * INTO SmallCust

FROM Customer

WHERE CreditLimit<=7500;

SQL - Data Definition I

• Create a database structure to hold all the database tables; MS Access ONLY can create tables

• Usually, only a DBA can create a new database structure

SQL syntax for creating a database structure:CREATE SCHEMA AUTHORIZATION <creator>;

Example:CREATE SCHEMA AUTHORIZATION JONES;

SQL - Data Definition II

• Specify a new relation by giving it a name and specifying each of its attributes.

• Each attribute is given a name, a data type to specify its values, and some constraints on the attribute.

• Syntax:

CREATE TABLE <table name>;

SQL Example – Data Definition

• Example 32: Save as example 32– Create a table call “CSUB” that contains following

fields:• EmpID Number (vs. Number(9) or Num(9))• LastName Char(20)• FirstName Char(20)• Street Char(30)• City Char(20)• State Char(2)• Phone Number

Example 32 (con’t)

Using AccessCreate table CSUB(EmpID Number, LastName Char(20), FirstName Char(20), Street

Char(30), City Char(20), State Char(2), Phone Number);

• Insert following values:– EmpID: 123456789– LastName: your lastname– FirstName: your firstname– Street: 9001 Stockdale Hgwy– City: Bakersfield– State: CA– Phone: 6616656691

Example 32

INSERT INTO Employee

VALUES ('987654321', 'Choi', 'Yong', '9001 Stockdale', 'Bakersfield', 'CA', '123456789');

Using OracleCREATE TABLE EMPLOYEE

(FNAME VARCHAR(15) NOT NULL,

LNAME VARCHAR(15) NOT NULL,

SSN CHAR(9) NOT NULL, BDATE DATE,

SEX CHAR,

SALARY DECIMAL(10,2),

SUPERSSN CHAR(9),

DEPTNO INT NOT NULL, PRIMARY KEY (SSN),

FOREIGN KEY (SUPERSSN) REFERENCES EMPLOYEE(SSN), FOREIGN KEY (DNO) REFERENCES DEPARTMENT(DNUMBER) );