SQL: Queries, Constraints, Triggers

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1 اصول طراحی پایگاه داده ها Principles of Database Design SQL: Queries, Constraints, Triggers مدرس : عاطفه خزاعی 1

2 زبان پرس و جوی SQL شرکت IBM در دهه 1970 در سیستم مدیریت پایگاهداده System R برای اولین بار از این زبان استفاده نمود. زمانی که توسط شرکتهای زیادی استفاده شد نیاز به استاندارد شدن پیدا کرد. SQL-86 SQL-89 SQL-92 SQL-99 SQL-2003 استانداردها: 2

3 زبان پرس و جوی SQL چند جنبه دارد: Data Definition Language (DDL): subset of SQL that supports creation, deletion, and modification of definitions for tables and views. Other aspects: define integrity constraints on tables; specify access rights or privileges to tables or views. (Chapter 3) Data Manipulation Language (DML): subset of SQL that allows users to pose queries and to insert, delete, and modify rows. (Chapter 3) 3

4 زبان پرس و جوی SQL چند جنبه دارد: Triggers and Advanced Integrity Constraints. (Chapter 5) Embedded and Dynamic SQL. (Chapter 6) Client-Server Execution and Remote Database Access. (Chapter 7) Transaction Management. (Chapter 21) Security. (Chapter 21) Advanced features: object-oriented features (Chapter 23), recursive queries (Chapter 24), decision support queries (Chapter 25), and also addresses emerging areas such as data mining (Chapter 26), spatial data (Chapter 28), and text and XML data management (Chapter 27). 4

5 جدول های مثال Sailors (sid: integer, sname: string, rating: integer, age: real) Boats (bid: integer, bname: string, color: string) Reserves (sid: integer, bid: integer, day: date)

6 bid bname color جدول های مثال Sid sname rating age Sid bid day

7 جداول قایقران ها قایق ها و رزرو

8 شکل پایه یک پرس و جوی SQL SELECT FROM WHERE )رابطه( مورد نظر [DISTINCT] target-list relation-list qualification :relation-list اسامی جداول :target-list لیست ستون ها یا صفت های مورد نظر OR یا AND شرایط برای انتخاب سطرهای خاص با انواع ترکیبات :qualification و یا,,,,, :DISTINCT برای حذف تکراریها در رابطه )جدول( خروجی به کار میرود. این کلمه کلیدی الزامی نیست اما در SQL در حالت عادی بر عکس عملگرهای رابطهای تکراریها را حذف نمیکند. 8

9 مثال ساده SQL Find the names and ages of all sailors. SELECT DISTINCT S.sname, S.age sname age sname age With DISTINCT Without DISTINCT 9

10 مثال ساده SQL Find all sailors with a rating above 7. SELECT S.sid, S.sname, S.rating, S.age FROM Sailors AS S WHERE S.rating > 7 10

11 Conceptual Evaluation Strategy استراتژی ارزیابی مفهومی SELECT FROM WHERE [DISTINCT] target-list relation-list qualification مفهوم یک جمله ساده SQL را می توان با یک استراتژی مفهومی به شکل زیر بیان نمود: Compute the cross-product of relation-list. Discard resulting tuples if they fail qualifications. Delete attributes that are not in target-list. If DISTINCT is specified, eliminate duplicate rows. البته این استراتژی برای اجرا بهینه عمل نمیکند. در سیستمهای پایگاهداده برای اجرا از استراتژیهایی برای بهینه نمودن اجرا استفاده میگردد. 11

12 Find the names of sailors who have reserved boat number 103. SELECT S.sname Sailors S, Reserves R FROM WHERE S.sid=R.sid AND R.bid=103 SELECT sname FROM Sailors, Reserves WHERE Sailors.sid=Reserves.sid AND bid=103

13 Find the colors of boats reserved by Lubber. SELECT B.color, Reserves R, Boats B WHERE S.sid = R.sid AND R.bid = B.bid AND S.sname = 'Lubber' 13

14 Find name of sailors who ve reserved at least one boat SELECT S.sname, Reserves R WHERE S.sid=R.sid Would adding DISTINCT to this query make a difference? What is the effect of replacing S.sid by S.sname in the SELECT clause? Would adding DISTINCT to this variant of the query make a difference? 14

15 Compute increments for the ratings of persons who have sailed two different boats on the same day. یک واحد به رتبه ملوانهایی که دو قایق مختلف را در یک روز رزرو کردهاند بیفزایید. SELECT S.sname, S.rating+1 AS rating, Reserves R1, Reserves R2 WHERE S.sid = R1.sid AND S.sid = R2.sid AND R1.date = R2.date AND R1.bid <> R2.bid تمرین: اجرای این پرس و جو واقعا به مقادیر رتبهی ملوانها نمیافزاید. چگونه این کار را انجام دهیم 15

16 Find the ages of sailors whose name begins and ends with B and has at least three characters. این دو امکان میتوان دادههای مورد نظر را دادن با LIKE و :NOT LIKE با یک رشته کاراکتری به عنوان کرد. نشانوند جستجو و بیان شرایط مورد نظر بازیابی SELECT S.age WHERE S.sname LIKE 'B%B' 16

17 عملگرهای مجموعه ای در SQL معادل اشتراک INTERSECT معادل اجتماع UNION معادل تفاضل EXCEPT 17

18 Find sid s of sailors who ve reserved a red or a green boat SELECT S.sid, Boats B, Reserves R WHERE S.sid=R.sid AND R.bid=B.bid AND (B.color= 'red' OR B.color= 'green') SELECT S.sid, Boats B, Reserves R WHERE S.sid=R.sid AND R.bid=B.bid AND B.color= 'red' UNION SELECT S.sid, Boats B, Reserves R WHERE S.sid=R.sid AND R.bid=B.bid AND B.color='green' UNION: Can be used to compute the union of any two union-compatible sets of tuples (which are themselves the result of SQL queries). If we replace OR by AND in the first version, what do we get?

19 Find sid s of sailors who ve reserved a red and a green boat SELECT S.sid, Boats B1, Reserves R1, Boats B2, Reserves R2 WHERE S.sid=R1.sid AND R1.bid=B1.bid AND S.sid=R2.sid AND R2.bid=B2.bid AND B1.color= 'red' AND B2.color='green' SELECT S.sid, Boats B, Reserves R WHERE S.sid=R.sid AND R.bid=B.bid AND B.color= 'red' INTERSECT SELECT S.sid, Boats B, Reserves R WHERE S.sid=R.sid AND R.bid=B.bid AND B.color='green' INTERSECT: Can be used to compute the intersection of any two union-compatible sets of tuples. Included in the SQL/92 standard, but some systems don t support it.

20 Find the sids of all sailor's who have reserved red boats but not green boats. SELECT R.sid FROM Boats B, Reserves R WHERE R.bid = B.bid AND B.color = red EXCEPT SELECT R2.sid FROM Boats B2, Reserves R2 WHERE R2.bid = B2.bid AND B2.color = green در MySQL به جای NOT EXIST EXCEPT را داریم 20

21 Find all sids of sailors who have a rating of 10 or reserved boat 104. SELECT S.sid WHERE S.rating = 10 UNION SELECT R.sid FROM Reserves R WHERE R.bid =

22 پرس و جوی تودرتو Query( )Nested A very powerful feature of SQL: typically a WHERE clause can itself contain an SQL query! (Sometimes appear in the FROM and the HAVING clauses.) Find names of sailors who ve reserved boat #103 SELECT S.sname WHERE S.sid IN (SELECT R.sid FROM Reserves R WHERE R.bid=103) 22

پرس و جوی تودرتو Query( )Nested Find names of sailors who ve not reserved boat #103 SELECT S.sname WHERE S.sid NOT IN (SELECT R.sid FROM Reserves R WHERE R.

23 پرس و جوی تودرتو Query( )Nested Find names of sailors who ve not reserved boat #103 SELECT S.sname WHERE S.sid NOT IN (SELECT R.sid FROM Reserves R WHERE R.bid=103) To find sailors who ve not reserved #103, use NOT IN. To understand semantics of nested queries, think of a nested loops evaluation: For each Sailors tuple, check the qualification by computing the subquery. 23

24 Find the names of sailors who have reserved a red boat. SELECT S.sname WHERE S.sid IN ( SELECT R.sid FROM Reserves R WHERE R. bid IN (SELECT B.bid FROM Boats B WHERE B.color = 'red' ) ) 24

25 Find the names of sailors who have not reserved a red boat. SELECT S.sname WHERE S.sid NOT IN ( SELECT R.sid FROM Reserves R WHERE R. bid IN (SELECT B.bid FROM Boats B WHERE B.color = 'red' ) ) IN, NOT IN? NOT IN, NOT IN? 25

26 Correlated Nested Queries Find names of sailors who ve reserved boat #103: SELECT S.sname WHERE EXISTS (SELECT * FROM Reserves R WHERE R.bid=103 AND S.sid=R.sid) EXISTS is another set comparison operator, like IN. 26

27 More on Set-Comparison Operators We ve already seen IN and EXISTS. Can also use NOT IN and NOT EXISTS. Also available: op ANY, op ALL, op IN,,,,, Find sailors whose rating is greater than that of some sailor called Horatio: SELECT * WHERE S.rating > ANY (SELECT S2.rating 2 WHERE S2.sname='Horatio') 28

28 More on Set-Comparison Operators Find sailors whose rating is greater than that of every sailor called Horatio: SELECT * WHERE S.rating > ALL (SELECT S2.rating 2 WHERE S2.sname='Horatio') 30

29 More on Set-Comparison Operators Find the sailor's with the highest rating. SELECT S.sid WHERE S.rating >= ALL ( SELECT S2.rating 2 ) 31

30 Rewriting INTERSECT Queries Using IN Find sid s of sailors who ve reserved both a red and a green boat: SELECT S.sid, Boats B, Reserves R WHERE S.sid=R.sid AND R.bid=B.bid AND B.color='red' AND S.sid IN (SELECT S2.sid 2, Boats B2, Reserves R2 WHERE S2.sid=R2.sid AND R2.bid=B2.bid AND B2.color='green') To find names (not sid s) of Sailors who ve reserved both red and green boats, just replace S.sid by S.sname in SELECT clause. (What about INTERSECT query?) Similarly, EXCEPT queries re-written using NOT IN. 32

31 Division in SQL Find sailors who ve reserved all boats. Let s do it without EXCEPT: (1) SELECT S.sname WHERE NOT EXISTS ((SELECT B.bid FROM Boats B) EXCEPT (SELECT R.bid FROM Reserves R WHERE R.sid=S.sid)) (2) SELECT S.sname WHERE NOT EXISTS (SELECT B.bid FROM Boats B WHERE NOT EXISTS (SELECT R.bid FROM Reserves R WHERE R.bid=B.bid AND R.sid=S.sid))

32 عمگرهای تجمیع Aggregate Operators افزایش چشمگیر در قابلیت های جبر رابطه ای COUNT (*) COUNT ( [DISTINCT] A) SUM ( [DISTINCT] A) AVG ( [DISTINCT] A) MAX (A) فقط نام یک ستون (A) MIN AVG ([DISTINCT] A): The average of all (unique) values in the A column. Find the average age of sailors with a rating of 10. SELECT AVG (S.age) WHERE S.rating=10? SELECT AVG ( DISTINCT S.age) WHERE S.rating=10

33 عمگرهای تجمیع Aggregate Operators MAX (A): The maximum value in the A column. COUNT (*) COUNT ( [DISTINCT] A) SUM ( [DISTINCT] A) AVG ( [DISTINCT] A) MAX (A) فقط نام یک ستون (A) MIN Find the name of sailor who have the max rating. SELECT S.sname WHERE S.rating= (SELECT MAX(S2.rating) 2)

34 نام و سن پیرترین قایقران )قایقران ها( Find the name and age of the oldest sailor. پرس و جوی اول اشتباه است! پرس و جوی سوم و دوم معادل هم هستند ولی برخی از سیستم ها پرس و جوی سوم را پشتیبانی نمیکنند. SELECT S.sname, MAX(S.age) SELECT S.sname, S.age WHERE S.age = (SELECT MAX(S2.age) 2) SELECT S.sname, S.age WHERE (SELECT MAX(S2.age) 2) = S.age

35 عمگرهای تجمیع Aggregate Operators COUNT ([DISTINCT] A): MIN (A) The number of (unique) values in the A column. COUNT (*) COUNT ( [DISTINCT] A) SUM ( [DISTINCT] A) AVG ( [DISTINCT] A) MAX (A) فقط نام یک ستون Count the number of sailors. SELECT COUNT(*)? SELECT COUNT(DISTINCT S.rating) WHERE S.sname='Bob' Count the number of different sailor names. SELECT COUNT( DISTINCT S.sname )

36 عمگرهای تجمیع Aggregate Operators COUNT (*) COUNT ( [DISTINCT] A) SUM ( [DISTINCT] A) AVG ( [DISTINCT] A) MAX (A) فقط نام یک ستون (A) MIN SUM ([DISTINCT] A): The sum of all (unique) values in the A column. MIN (A): The minimum value in the A column.

37 Find the names of sailors who are older than the oldest sailor with a rating of 10. SELECT S.sname WHERE S.age > ( SELECT MAX(S2.age ) 2 WHERE S2.rating = 10 ) SELECT S.sname WHERE S.age > ALL ( SELECT S2.age 2 WHERE S2.rating = 10 ) 39

38 Motivation for Grouping در مواردی ممکن است بخواهیم توابع تجمیع را برای گروههای مختلف به صورت مجزا داشته باشیم مثال: میانگین نمرات درس پایگاه داده برای هر ورودی مثال: برای هر سطح امتیاز level( )rating جوانترین قایقران را پیدا کنید. راه حل سریع: به ازای هر سطح امتیاز جوانترین قایقران را مییابیم For i = 1, 2,..., 10: SELECT MIN (S.age) WHERE S.rating = i اما نمی دانیم که چند سطح امتیاز داریم 40

پرس وجو با GROUP BY و HAVING SELECT FROM relation-list WHERE qualification GROUP BY grouping-list HAVING group-qualification [DISTINCT] target-list )MIN(S.

39 پرس وجو با GROUP BY و HAVING SELECT FROM relation-list WHERE qualification GROUP BY grouping-list HAVING group-qualification [DISTINCT] target-list )MIN(S.age) target-list لیست ستونهای مورد نظر عبارت هایی با عملیات )مثال تجمیع لیست ستونها باید یک زیرمجموعه از grouping-list باشد و سطر خروجی )پاسخ( مربوط به یک گروه خاص است. باید دقت کرد که مواردی که در target-list می آید به ازای هر گروه باید یک مقدار داشته باشد. نام ستونی که داخل یک عملیات تجمیع میآید میتواند هر یک از ستونهای جدول باشد الزامی نیست که از grouping-list باشد. یک گروه مجموعهای از سطرهایی است که مقادیری یکسان برای همهی صفات grouping-list دارند. 41

40 Find the age of the youngest sailor for each rating level. SELECT S.rating, MIN(S.age) GROUP BY S.rating لیست ستونهای مورد نظر و عبارتهایی با عملیات تجمیع لیست ستونها باید در grouping-list بیاید و به ازای هر گروه باید یک مقدار داشته باشد 42

41 سن جوانترین قایقران از میان قایقران های باالی 18 سال برای هر رده امتیاز که حداقل 2 ملوان در آن گروه باشند. SELECT S.rating, MIN(S.age) AS minage WHERE S.age >= 18 GROUP BY S.rating HAVING COUNT(*) > 1 Answer relation: rating minage Sailors instance: sid sname rating age 22 dustin brutus lubber andy rusty horatio zorba horatio art bob frodo

42 اجرای پرس و جوی قبل Find age of the youngest sailor with age>=18, for each rating with at least 2 such sailors. rating age rating age rating minage

43 Find age of the youngest sailor for each rating with at least 2 sailors between 18 and 60. SELECT S.rating, MIN(S.age) AS minage WHERE S.age >= 18 AND S.age <= 60 GROUP BY S.rating HAVING COUNT(*) > 1 Answer relation: rating minage Sailors instance: sid sname rating age 22 dustin brutus lubber andy rusty horatio zorba horatio art bob frodo

Database Management Systems. Chapter 5

Database Management Systems. Chapter 5 Database Management Systems Chapter 5 SQL Example Instances We will use these instances of the Sailors and Reserves relations in our examples. If the key for the Reserves relation contained only the attributes