Beginning SQL

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includes that record. You should always remember that SQL is set-based and compares all records in each set to all the records in the other sets. Reducing set size in WHERE clauses is also worthwhile, because smaller sets compare fewer records, which increases the efficiency of queries. That’s it for this section. The next section delves into the unknown! Introducing NULL Data In the sections leading up to this one, you’ve dealt strictly with known data, but often that’s not possible. Given that statement, you might assume that data with no specified value has no value at all. SQL, however, doesn’t allow for data to hold no value. Fields with no specified value actually do have a value: NULL. NULL is not the same thing as nothing; NULL represents the unknown. If you were asked how many hairs there are on your head, unless you’re bald, you’d have to say that you don’t currently know. There is a value, and one day you might know it and be able to store it in a database, but right know it’s unknown. This is where NULL comes into play. NULL represents, and allows you to search for, unknown values. The following is a SQL statement that inserts a new record into the MemberDetails table. Execute the statement in your own database: INSERT INTO MemberDetails (MemberId, FirstName, LastName, Email, DateOfJoining) VALUES (15, ‘Catherine’,’Hawthorn’, ‘chawthorn@mailme.org’, ‘2005-08-25’) The MemberDetails table contains DateOfBirth, Street, City, and State fields, yet the SQL doesn’t specify any values for these fields. This is perfectly acceptable, so the question is, what values are contained in the fields where no value is specified? You might suggest that because you specified no values, the values in those fields are no value, or nothing at all. In fact, the database system considers the value not to be nothing but instead to be unknown, or NULL. You might be wondering why you should care about all this. First of all, NULLs can lead to unexpected and overlooked results. For example, you might think that the following SQL would return all the records in the MemberDetails database: SELECT FirstName, LastName, DateOfBirth FROM MemberDetails WHERE DateOfBirth ‘1970-01-01’; Extracting Information After all, the statement selects all dates of birth on or before January 1, 1970, and also after January 1, 1970, and yet the record just added to the database for Catherine Hawthorn is not there because the date of birth is NULL (see the following table). Don’t forget to change the date format for Oracle and the single quotes to hash marks (#) for Access in the preceding SQL. 113
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Beginning SQL Paul Wilton and John
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Beginning SQL Paul Wilton and John
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About the Authors Paul Wilton After
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Paul Wilton: With lots of love to m
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Contents x Selecting Correct Data T
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Contents xii Re-examining NULL 180
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Contents Chapter 11: Transactions 3
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Contents xvi How Do You Do It? 357
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Introduction Data, data, data! Data
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By the time you’ve completed Chap
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Once you download the code, just de
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1 Introduction to SQL A nice, gentl
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Figure 1-1 Why and When to Use a Da
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Databases are great at dealing with
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The SQL language is actually fairly
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you wish, and the database system d
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A keyword is a word that has some m
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Introduction to SQL A perfectly val
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Data Type Description Storage Used
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The char and varchar data types use
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Most RDBMSs handle the most common
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To add a new column, use the basic
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Now that you know what you want to
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❑ Meeting date 2 ❑ Location 2
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Generally speaking, picking a data
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example, the MemberId field links t
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Depending on which RDBMS you’re u
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The FilmCategory table is very smal
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2 Entering Information The last cha
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like this: INSERT INTO Category VAL
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Inserting Data into the Case Study
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The WHERE Clause So far you’ve se
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Try It Out Using Logical Operators
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Exercises 1. Three new members have
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Chapter 3 54 MemberId FirstName 1 K
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Chapter 3 The results are as follow
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Chapter 3 The results to this query
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Chapter 3 FavCategory (CategoryId,
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Chapter 3 Logical Operators and Ope
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Chapter 3 The statement returns the
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Chapter 3 NOT Operator Examples thu
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Chapter 3 2. Using the following SQ
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Chapter 3 When you execute the quer
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Chapter 3 Now that you’re acquain
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Chapter 3 It’s as simple as that!
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Chapter 3 76 YearReleased 1947 1967
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Chapter 3 78 FilmName Rating Gone w
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Chapter 3 2. Add a WHERE clause to
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Chapter 3 Executing this SQL provid
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Chapter 3 84 FullName First name is
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Chapter 3 86 FullName First name is
Page 216: Chapter 3 Even though DateOfBirth i
Page 220: Chapter 3 Member Name The member is
Page 224: Chapter 3 92 The preceding SQL prod
Page 228: Chapter 3 94 ❑ Category ❑ FavCa
Page 232: Chapter 3 96 You’re one step furt
Page 236: Chapter 3 98 FirstName LastName Cat
Page 240: Chapter 3 This time, you achieve mo
Page 244: Chapter 3 SQL Is Set-Based 102 You
Page 248: Chapter 3 104 Category MemberId Thr
Page 252: Chapter 3 106 You should see the fo
Page 256: Chapter 3 The overlapping portions
Page 260: Chapter 3 110 More than one conditi
Page 264: Chapter 3 112 Next, link the Member
Page 270: FirstName LastName DateOfBirth Jenn
Page 274: 4 Advanced Database Design This cha
Page 278: Date of Date Meeting Did Member Nam
Page 282: Now the tables are in second normal
Page 286: After changing the database so that
Page 290: IBM’s DB2 doesn’t allow you to
Page 294: The following code creates a new ta
Page 298: If you’re using DB2, the code is
Page 302: The NOT NULL constraint prevents th
Page 306: In the preceding code, CustomerId i
Page 310: Foreign Key Foreign keys are column
Page 314: MemberId MeetingDate Street City St
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The third step had you create the p
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The results are ordered because, by
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The index is no longer needed, so d
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WHERE MemberAttended = ‘Y’; DRO
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Primary keys must be unique and can
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Then add the PRIMARY KEY constraint
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( ); FilmId integer NOT NULL, FilmN
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ALTER TABLE Attendance ADD CONSTRAI
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❑ You learned the importance of e
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Chapter 5 158 Function Operator Mul
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Chapter 5 Consider the following SQ
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Chapter 5 The SQRT() Function The S
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Chapter 5 164 chairperson now also
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Chapter 5 The FLOOR() Function The
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Chapter 5 DVDPrice ROUND(DVDPrice,1
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Chapter 5 Note that, as with all th
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Chapter 5 The TRIM() Functions Trim
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Chapter 5 174 In Oracle and IBM’s
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Chapter 5 176 FirstName SOUNDEX(Fir
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Chapter 5 Date Functions 178 Someti
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Chapter 5 The syntax for the CAST()
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Chapter 5 NULLs and Strings 182 NUL
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Chapter 5 184 SELECT FirstName, Las
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Chapter 5 186 This SQL copies over
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Chapter 5 You also learned that mat
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Chapter 6 190 Begin by looking at h
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Chapter 6 This section covers queri
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Chapter 6 194 This query gives the
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Chapter 6 You’re almost there. Yo
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Chapter 6 the database even though
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Chapter 6 SELECT Category, AVG(DVDP
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Chapter 6 Try It Out Selecting Data
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Chapter 6 SELECT Category, COUNT(Fa
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7 Selecting Data from Different Tab
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Selecting Data from Different Table
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Note that MS Access insists that yo
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City State Orange Town New State Wi
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SELECT FM1.FilmName FROM Films AS F
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Selecting Data from Different Table
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effects of any WHERE clause. There
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Now re-execute the query. You get a
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the category list and a list of whi
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Category FirstName LastName Horror
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You can join the results from two o
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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function and the query still works,
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Summary Selecting Data from Differe
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Chapter 8 A WHERE clause is added t
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Chapter 8 238 FilmName PlotSummary
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Chapter 8 If you think that your jo
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Chapter 8 In the query, the Categor
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Chapter 8 244 There is one area in
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Chapter 8 246 SELECT FirstName, Las
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Chapter 8 248 The subquery (SELECT
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Chapter 8 250 Notice the use of the
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Chapter 8 4. You should receive the
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Chapter 8 254 This inner query retu
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Chapter 8 It’s quite important no
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Chapter 8 258 To tackle this query,
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Chapter 8 260 Now you need to find
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9 Advanced Queries In database prog
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FOREIGN KEY (OrderId) REFERENCES Or
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INSERT INTO Orders(OrderId, MemberI
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INSERT INTO OrderItems(OrderId,Film
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A more complex question could be,
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Advanced Queries What you really wa
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FirstName and LastName. You need to
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2. The film club chairperson also w
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Executing the preceding query provi
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GROUP BY SalesPerson.SalesPersonId,
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Executing the preceding SQL creates
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❑ Use IN with your subqueries. Wh
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10 Views Views, as the name implies
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Try It Out Building a View 1. The p
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FROM dbo.MemberDetails INNER JOIN d
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For example, you might want a list
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However, if you take the case of Me
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However, someone writes a query tha
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Summary As you learned, views are l
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Chapter 11 The information that fol
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Chapter 11 This SQL adds formats (d
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Chapter 11 TRANSACTION statement is
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Chapter 11 Additionally, if a DBMS
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Chapter 11 ROLLBACK TRANSACTION 310
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Chapter 11 Transaction Logs 312 How
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Chapter 11 Database There are perfe
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Chapter 11 In order to find and fix
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Chapter 11 When discussing locking,
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Chapter 11 Usually, the default iso
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Chapter 11 From Sue’s perspective
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Chapter 11 5. At this point, you ne
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12 SQL Security In today’s world,
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Setting up security begins with cre
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ALTER USER username options ALTER U
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In Figure 12-3, three different gro
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How It Works After you run this sta
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check constraints can be used in a
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You could then give SELECT privileg
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Limitations on Views Views are by t
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GRANT SELECT (NAME, SSN, SALARY) ON
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Betsey also grants privileges to Ji
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The CASCADE option tells the DBMS t
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13 Database Tuning SQL is a languag
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Perhaps this doesn’t sound remote
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When an application asks for data f
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The point of all the discussion of
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How Do You Do It? And herein lies t
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The slots are often implemented as
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On the other hand, an index on a tr
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Tuning Tips The following list cont
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Database Tuning Exercises 1. Create
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Appendix A Exercise 2 Solution 368
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Appendix A ( 8, ‘Jack’, ‘John
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Appendix A ZipCode, Email, DateOfJo
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Appendix A Exercise 3 Solution Firs
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Appendix A 376 Figure A-1 ISBN is a
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Appendix A Chapter 5 Exercise 1 Sol
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Appendix A 380 You might receive sl
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Appendix A 382 You should use the f
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Appendix A Your answer may differ,
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Appendix A WHERE (SELECT COUNT(*) f
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Appendix A Exercise 2 Solution CREA
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Appendix A Chapter 13 Exercise 1 So
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Appendix B 392 Click the database i
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Appendix B 394 Click Install to beg
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Appendix B 396 Select the Detailed
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Appendix B 398 Leave it at the defa
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Appendix B 400 Having entered your
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Appendix B 402 Figure B-20 The inst
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Appendix B 404 At the very top of t
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Appendix B 406 Having done that, ma
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Appendix B 408 Figure B-30 MyTable
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Appendix B 410 Figure B-32 Click Ne
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Appendix B 412 Click Next to contin
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Appendix B 414 Click OK to clear th
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Appendix B If you’re ready and ha
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Appendix B 418 You can also enter a
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Appendix B 420 Figure B-49 The Film
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Appendix B 422 Now you need to inse
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Appendix B 424 In Access it’s not
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Appendix B 426 Figure B-56 You need
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Appendix B 428 Then click the Run i
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Appendix B 430 The next screen (see
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Appendix B 432 On the next screen,
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Appendix B 434 Click Next to procee
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Appendix B 436 Figure B-72 The huge
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Appendix B 438 Figure B-74 Notice t
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Appendix B 440 Figure B-76 The Obje
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Appendix B 442 Figure B-78 Chapter
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Appendix B You don’t need MyTable
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Appendix B 446 Figure B-82 To begin
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Appendix B Using Oracle’s SQL*Plu
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Appendix B 450 Figure B-87 Another
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Appendix C Category Table The follo
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Appendix C 454 ( 3, ‘Sandra’,
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Appendix C 456 ZipCode, Email, Date
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Appendix C DateOfJoining ) VALUES (
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Appendix C 460 VALUES ( 1, 3 ); INS
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Appendix C VALUES ( 5, 3 ); INSERT
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Appendix C 464 3 ); INSERT INTO Fil
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Appendix C 5, 6 ); INSERT INTO Film
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Appendix C 468 5 ); INSERT INTO Att
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Appendix C Oracle 470 To save some
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Appendix C 472 LocationId, MeetingD
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Symbols + (addition operator), 82,
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BEGIN TRANSACTION statement, 306, 3
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SERIALIZABLE statement, 318 SET TRA
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data types brackets, 25 categories,
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Oracle concatenation, 85-88 configu
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error messages debugging, 26 subque
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concatenation, 85-88 data type comp
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primary keys database creation exam
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concurrent connection selection, 39
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passwords group access, 333 IBM ins
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ROLLBACK statement, 307-308 ROLLBAC
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REPEATABLE READ, 319 REVOKE, 344-34
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telephone numbers, data type select
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historical, data selection, 90-94 N
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