Beginning SQL

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Shared A shared lock essentially means that no one can modify the data, but other users may look at and use the data for any purpose not requiring an update. A user may need to run a report that asks different questions about a set of records. If any of those records were to be updated by another user, then the questions would not provide consistent answers since the data provided at the end would not be the same as the data at the beginning. On the other hand, it is perfectly valid for other users to ask questions about that same set of data. It is not necessary to lock the data such that no one else can see it. Exclusive An exclusive lock means that other users should not be allowed to see the data because the data is about to be changed. If one user is updating the price of every inventory item by 5 percent and another user is running a report about the value of all the items in the inventory, the report would return a different answer depending on when the report started running and how many items had already been updated. Deadlocks If you think about users locking different records in different tables, it becomes obvious that the database could get in a situation where user 1 is waiting for data locked by user 2, and user 2 is waiting for data locked by user 1. Each user needs the data locked by the other user before they can finish their process and release their locks. This situation is known as a deadlock. Deadlocks inevitably occur, and the DBMS must have a means to identify a deadlock and then must have a strategy for breaking the deadlock and allowing one of the users to gain control of the data they need in order to release the locks they applied. Unless the DBMS intervenes, both user requests wait forever for the other to unlock the necessary data. This is a simple two-way deadlock, but of course deadlocks can occur between many different users at once. Figure 11-7 shows a situation where two different transactions have locks applied, and each is waiting for the data locked by the other transaction in order to continue. Transaction A has locked record 2 in the Products table, and Transaction B is waiting to use record 2 in the Products table. Transaction B has locked record 79 in the Orders table, and Transaction A is waiting for record 79 in the Orders table. Neither transaction can continue until it gains control of the record locked by the other transaction. Transaction A Locks Record 2 Waiting for rec 79 in order to finish Figure 11-7 1 2 3 4 5 6 7 78 79 80 81 82 83 84 85 Products Orders Transaction B Waiting for rec 2 in order to finish Locks Record 79 Transactions 315
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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
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Chapter 3 Even though DateOfBirth i
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Chapter 3 Member Name The member is
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Chapter 3 92 The preceding SQL prod
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Chapter 3 94 ❑ Category ❑ FavCa
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Chapter 3 96 You’re one step furt
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Chapter 3 98 FirstName LastName Cat
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Chapter 3 This time, you achieve mo
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Chapter 3 SQL Is Set-Based 102 You
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Chapter 3 104 Category MemberId Thr
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Chapter 3 106 You should see the fo
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Chapter 3 The overlapping portions
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Chapter 3 110 More than one conditi
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Chapter 3 112 Next, link the Member
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Chapter 3 114 FirstName LastName Da
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Chapter 3 ❑ The slightly tricky t
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Chapter 4 normalization can make da
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Chapter 4 120 Field Name Data Type
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Chapter 4 122 The Street, City, and
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Chapter 4 MySQL versions prior to 5
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Chapter 4 126 Except for IBM’s DB
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Chapter 4 128 You can add more than
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Chapter 4 Try It Out Adding a CHECK
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Chapter 4 Obviously, if the table i
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Chapter 4 134 Drop the MoreHolidayB
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Chapter 4 136 If you want to return
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Chapter 4 If you’re using IBM DB2
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Chapter 4 140 index helps speed up
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Chapter 4 142 The results you get m
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Chapter 4 144 The results of the qu
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Chapter 4 146 Remember, IBM DB2 doe
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Chapter 4 148 UPDATE Films SET Film
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Chapter 4 150 Finally, you do the s
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Chapter 4 152 SELECT * FROM MemberD
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Chapter 4 ❑ Choose meaningful nam
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5 Manipulating Data In Chapter 3, y
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The results of this query are as fo
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You can raise a number to any power
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To demonstrate the sort of results
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The CEILING() Function The CEILING(
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ased on the digits after the decima
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The SUBSTRING() function works at t
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LastName UPPER(LastName) LOWER(Last
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The LENGTH() function takes just on
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LastName LOWER(SUBSTRING(LastName,1
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FirstName DIFFERENCE(FirstName, ‘
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Converting Different Data Types Thi
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CREATE Table MyTable(FirstColumn in
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The COALESCE() Function The COALESC
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Ideally, this first argument is the
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LocationId Street City State 1 Main
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6 Grouping and Aggregating Data So
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Running the query, complete with a
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MemberId Street City State 11 Newis
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Executing the SQL returns seven dis
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For example, the following code add
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Running the query gives the answer
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SELECT MAX(LastName), MIN(LastName)
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immediately after the GROUP BY stat
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Executing the final SQL provides th
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Chapter 7 The INNER JOIN links the
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Chapter 7 FilmName FirstName LastNa
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Chapter 7 212 As mentioned, that wo
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Chapter 7 Category Street Romance T
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Chapter 7 216 MD1.First MD1.Last MD
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Chapter 7 SELECT MD1.MemberId, MD1.
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Chapter 7 220 SELECT Category, Film
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Chapter 7 222 Location.Street Membe
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Chapter 7 224 Category MemberId War
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Chapter 7 Look at the results that
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Chapter 7 228 The Maltese Poodle 8
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Chapter 7 230 9 10 11 12 13 14 15 1
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Chapter 7 232 On Golden Puddle 1967
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8 Queries within Queries This chapt
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There are no films with a value in
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The error wording depends on the da
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Now execute the query. You receive
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The query provides the following re
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If you execute this query, you can
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To obtain the same results as you w
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MemberId 1 10 14 6 5 8 7 11 15 4 13
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Now NOT EXISTS returns true, and as
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This is the same as the query just
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clause specifying that the film’s
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4. Next, quickly double-check a few
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Now that you’ve confirmed that th
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Summary Queries within Queries This
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Chapter 9 264 Figure 9-1 The SQL ne
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Chapter 9 266 INSERT INTO OrderItem
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Chapter 9 268 VALUES (5,7, 2,’200
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Chapter 9 Now that you’ve added t
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Chapter 9 272 FirstName LastName Mo
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Chapter 9 274 DVDPrice column is in
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Chapter 9 SalesPersonId FirstName L
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Chapter 9 278 SalesPersonId MemberI
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Chapter 9 280 SalesPersonId MemberI
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Chapter 9 282 MemberDetails.FirstNa
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Chapter 9 284 The query would work
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Chapter 9 Exercises 286 Assume that
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Chapter 10 Now that you know what v
Page 620: Chapter 10 Types of Views Given tha
Page 624: Chapter 10 Perhaps you need to view
Page 628: Chapter 10 Figure 10-7 Summary view
Page 632: Chapter 10 296 This statement gives
Page 636: Chapter 10 The CHECK OPTION plays a
Page 642: 11 Transactions When you move out o
Page 646: Example Data This section creates e
Page 650: 3. Build a record in the Rentals ta
Page 654: The other statement that the ANSI S
Page 658: SAVE TRANSACTION Select Update Begi
Page 662: Figure 11-5 Begin Transaction Delet
Page 666: In spite of all of these performanc
Page 672: Chapter 11 In order to find and fix
Page 676: Chapter 11 When discussing locking,
Page 680: Chapter 11 Usually, the default iso
Page 684: Chapter 11 From Sue’s perspective
Page 688: Chapter 11 5. At this point, you ne
Page 694: 12 SQL Security In today’s world,
Page 698: Setting up security begins with cre
Page 702: ALTER USER username options ALTER U
Page 706: In Figure 12-3, three different gro
Page 710: How It Works After you run this sta
Page 714: check constraints can be used in a
Page 718: 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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