CIS 451: SQL

Dr. Ralph D. WestfallFebruary, 2009

What Is SQL? Structured Query Language standard data access language for

relational databases (RDBMS) RDBMS dominate market

Access, Oracle, Sybase, DB2, SQL Server, etc.

SQL Standardization Advantages greater productivity

reduced training costs application portability less dependence on specific vendors easier integration of separate systems

adapted from McFadden & Hoffer, 1994

Can Put SQL Into Programs "embedded" SQL can go into code

in C, C++, C# Java Perl, Tcl COBOL, FORTRAN, Ada Visual Basic.NET ASP.NET

SQL Command Types data manipulation language (DML) works

with records and fields get raw data from table(s) in

database(s) get summary data (total, average, count,

etc.) add, change, or delete records

data definition language (DDL) works with tables create, change, or delete tables create or delete indexes

SQL Command Parts (DML) manipulative – tell what to do

SELECT … FROM – get records INSERT INTO … – add records DELETE FROM … – removes records UPDATE … SET … – change records

SQL Command Parts - 2 options declarations – tell where

and how the action will occur WHERE – sets conditions (like an IF

clause) ORDER BY – sets sort order e.g.,

ascending GROUP BY – useful when combining

data e.g., total or average for each separate item, such as sales by salespersons or countries

SQL Command Parts - 3 parameter declarations

optional at start (before manipulative part) contain values passed into the query

like parameters in a subprocedure

SQL Select Command SELECT [field list] FROM [table list}SELECT * FROM Customer

get all fields from Customer tableSELECT Name, Address FROM Customer get only Name and Address fieldsSELECT [Zip Code] FROM Customer use square brackets if space(s) in

a name

Sorting

SELECT * FROM Sales ORDER BY Date sorted ascending (from earliest to

latest)SELECT Name, City FROM Students _

ORDER BY City sorted ascending (alphabetically: A to

Z)

Sorting - 2SELECT Product, Price FROM Sales _ORDER BY Price DESC, Quantity

Price sorted descending (highest first) when Price is same, then sorted

ascending by Quantity (lowest to highest)

Product Price [Quantity]carrot 0.29[7]radish 0.27[2]beet 0.27[3]corn 0.25[1]

"Filter" Conditions tell which records to include in

results WHERE logical-expression test-valueWHERE Count < 10

6 comparison operators in SQL< less than <= less than or equal= equal <> not equal> greater >= greater than or equal

Filter Conditions - 2 special "predicates"WHERE Name LIKE 'Ng*'

WHERE State IN ('CA', 'NY')

WHERE Count BETWEEN 1 AND 5

Wild Cards in Filter Conditions * one or more characters: s* so, solitude ? single character: st?r star, stir # single digit: #123 9123 7123

0123 [start-end] characters: [b-d]ot bot cot dot [letters]: [cfhms]at cat fat hat mat sat ! not: b[!au]ll bell bill boll (not ball or bull) combination: [mt]o?n* moonlight tornado

Getting Calculated Fields calculation operators used on fields

SELECT Quantity * Price FROM Orders

SELECT FirstName & ' ' & LastName …

'concatenates names together with space system creates name for above

examples can specify name for new field

SELECT FirstName & ' ' & LastName _

AS WholeName FROM Students

Getting Calculated Fields - 2 functions used on fields

Avg (average), Count, Min (smallest), Max (largest), Sum (total), etc.

SELECT Sum(Quantity) FROM Orders

SELECT Max(Quantity * Price) _

FROM Orders

Grouping to Summarize can use functions with GROUP BY

to get summary valuesSELECT State, Sum(Quantity) _FROM Orders GROUP BY State gets totals: 1 record for each state

with dataSELECT State, City, Sum(Quantity) _FROM Orders GROUP BY State, City total for each city with data, by state

Creating Table from a Query

SELECT Name, Phone INTO Locals _

FROM Clients WHERE City='Pomona'

creates a new table named Locals with selected data from other table

Using Parameters

PARAMETERS strCity String; _

SELECT * FROM Clients _

WHERE City=strCity

put Parameters at start, ending with ;

passed in variable value is substituted into query

Selecting from Multiple Tables need to identify

fields tables relationship between tablesSELECT Students.Name, Class, Grade _

FROM Students, Courses _

WHERE Students.SSNo = Courses.SID can identify tables for all fields if > 1

table

Multiple Table Relationships inner join

at least 1 field matches in both databases

SELECT Students.Name, Class, Grade _

FROM Students, Courses _

Students INNER JOIN Courses

ON Students.SSNo = Courses.SID to get a record, a value for SSNo in

Students table must be same as a value for SID in Courses table

Multiple Tables - 2 inner join (continued)

results table contains data from both tables in

each row WHERE clause can also create an inner

join, if it matches fields in separate tables

WHERE Students.SSNo = Courses.SID

Multiple Tables - 3 outer join

gets all records, even if don't match on the field

MS Access allows outer joins on only 1 side

tables could get very large if outer join on both

left join – all records from left table, matching records from other (right) table

right join – all records from right table

Multiple Tables - 4 one-sided (left or right) outer join

syntaxSELECT Employees.Name, Orders.Product

FROM Employees LEFT JOIN Orders ON

Employees.Emp_ID=Orders.Emp_ID results show all employees (left

table), even ones who haven't ordered any products yet (from W3Schools)

SQL Insert Command INSERT INTO Product _ (ProdID, Product, Price, InStock) _ VALUES ('0008', 'snark', 6.99, 120)

adds a record first set of parentheses enclose field

names second set of parentheses enclose

field values have to be in exactly the same order

ProdID is '0008' … Instock is 120

SQL Update Command UPDATE Product SET Instock = 20 _ WHERE ProdID = '0001'

updates value of Instock field to 20 for the record whose key value (ProdID field) is 0001

SQL Delete Command DELETE FROM Product _ WHERE ProdID = '0008'

deletes the record from Product table whose key value (ProdID field) is 0008

Data Definition Commands CREATE TABLE Students (SID LONG, _ FirstName TEXT (15), LastName TEXT _ (20), City TEXT (20))

creates a new table need to provide table name, fields,

and data types/field lengths

Data Definition Commands - 2 ALTER TABLE Students _ ADD COLUMN Street TEXT (30), Zip SINGLE

adds columns (fields) identify table, provide column

(field) name(s) and data types/field length(s)

Data Definition Commands - 3 DROP TABLE VAXComputers

deletes table need to identify table name

Data Definition Commands - 4 CREATE INDEX SIndex _ ON Students (SID) creates an index on the SID field in

table Students CREATE INDEX CIndex _ ON Circulation (BorrowerNo, BookNo) creates an index on two fieldsDROP INDEX CIndex

deletes index

Indexes sorted table of locations of keys to

records faster access to data slower updates

SQL Exercises online exercises at SQLCourse.com

exercises start: slide 2 ("Select Statement")

modify each exercise slightly switch order of fields other changes: fields selected, = vs. <>

paste each of your queries, followed by its results from SQL Interpreter, into a text file

then paste it into a Discussion Board message