1. CH 9 SQL 9.1 Querying A Single Table 9.2 Querying Multiple Tables
9.3 Changing Data

2. SQL(Structured Query Language)
Endorsed by ANSI(American National Standard Institute)
Data access language used by DB2, SQL/DS, ORACLE, INGRES, SYBASE, SQL Server, dBASE for Windows, Paradox, Microsoft Access
The development of SQL began at IBM’s San Jose research facilities in mid-1970s under the name SEQUEL
In 1980 the product was renamed SQL
SQL92(CH. 9 discuss this version)-1992
SQL3 (Most recent version, discussed in CH. 17)- 1997
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3. SQL’s commands and expressions
SQL is not a programming language; rather it is a data sub-language, or data access language, that is embedded in other languages
Expressions may differ in minor ways from the ANSI standard (e.g. Oracle or SQL Server)
SQL commands can be used interactively as a query language
Can be embedded in application programs
CH 9 only concerned with data manipulation statements (although there are also SQL commands for data definition and control)
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4. 9.1 Querying A Single Table
9.1.1 SQL Projections
9.1.2 SQL Selection
9.1.3 Sorting
9.1.4 Built-in function
9.1.5 Grouping
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5. Figure 9-1 SQL Example Relations 1. JUNIOR (Snum, Name, Major)
2. HONOR-STUDENT (Number, Name,Interest)
3. STUDENT (SID, Name, Mahor, GradeLevel,
Age)
4. CLASS (NAME, Time, Room)
5. ENROLLMENT (StudentNumber, ClassName,
PositionNumber)
6. FACULTY (FID, Name, Department)
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7. Sample data used for SQL example (a) STUDENT Relation
100
JONES
HISTORY GR 21
150
PARKS
ACCOUNTING SO 19
200
BAKER
MATH 50
250
GLASS SN
300 41
350
RUSSELL JR 20
400
RYE FR 18
450 24
SID Name Major GradeLevel Age
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8. (b) ENROLLMENT (c) CLASS StudentNumber ClassName PositionNumber
100
BD445 1
150
BA200
200 2
CS250
300
CS150
400
BF410
450 3
StudentNumber ClassName PositionNumber
(c) CLASS
BA200
M-F9
SC110
BD445
MWF3
SC213
BF410
MWF8
CS150
EA304
CS250
MWF12
EB210
Name Time Room
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9. 9.1.1 Projections Using SQL
Name the relation to be projected and list the columns to be shown
Projection : STUDENT[SID, Name, Major]
Standard SQL:
SELECT SID, Name, Major
FROM STUDENT
Result:
100
JONES
HISTORY
150
PARKS
ACCOUNTING
200
BAKER
MATH
250
GLASS
300
350
RUSSELL
400
RYE
450
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10. 9.1.1 Projections Using SQL Ex.: output contains duplicated rows
SELECT Major
FROM STUDENT
HISTORY
ACCOUNTING
MATH
Ex.: Duplicated rows are removed
SELECT DISTINCT Major
FROM STUDENT
HISTORY
ACCOUNTING
MATH
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11. 9.1.2 Selections Using SQL Ex.: Selecting all attributes
SELECT SID, Name, Major, GradeLevel, Age
FROM STUDENT
WHERE Major = 'MATH'
Ex.: * means that all columns of the table are to be obtained
SELECT *
200
BAKER
MATH GR 50
350
RUSSELL JR 20
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12. Ex.: Selection and Projection SELECT Name, Age FROM STUDENT
WHERE Major = 'MATH'
BAKER
RUSSELL 50 20
Ex.: Several conditions in the WHERE clause
SELECT Name, Age
FROM STUDENT
WHERE Major = 'MATH' AND Age > 21
BAKER 50
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13. Ex.: conditions in WHERE clause can refer to a set of values
- Key Word: IN or NOT IN
SELECT Name
FROM STUDENT
WHERE Major IN ['MATH', 'ACCOUNTING']
PARKS
BAKER
RUSSELL
RYE
Ex.: Display the names of students who have either a math or an accounting major
SELECT Name
FROM STUDENT
WHERE Major NOT IN ['MATH', 'ACCOUNTING']
JONES
GLASS
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14. WHERE Age > 19 AND Age < 30
Ex.: conditions in WHERE clause can refer to ranges and to partial values
- Key Word: BETWEEN
SELECT Name, Major
FROM STUDENT
WHERE Age BETWEEN 19 AND 30
JONES
HISTORY
RUSSELL
MATH
Ex.: Equivalent to
SELECT Name, Major
FROM STUDENT
WHERE Age > 19 AND Age < 30
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15. Ex.: LIKE can be used to select on partial values
‘_’ represent a single unspecified character
‘%’ represents a series of one or more unspecified characters
- Key Word: LIKE
SELECT Name, GradeLevel
FROM STUDENT
WHERE GradeLevel LIKE ‘_R’
JONES GR
BAKER
RUSSELL JR
RYE FR
Ex.: fond students whose last names end with S
SELECT Name
FROM STUDENT
WHERE Name LIKE ‘%S’
JONES
PARKS
GLASS
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16. ‘?’ represent a single unspecified character
Ex.: MS Access uses a different set of wildcard symbols than the ANSI standard
‘?’ represent a single unspecified character
‘*’ represents a series of one or more unspecified characters
Keyword IS NULL are used to search for null values
SELECT Name
FROM STUDENT
WHERE GradeLevel IS NULL
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17. 9.1.3 Sorting
The rows of the result relation can be sorted by the values in one or more columns
Ex.:
SELECT Name, Major, Age
FROM STUDENT
WHERE Major = 'ACCOUNTING'
ORDER BY Name
BAKER
ACCOUNTING 41
PARKS
RYE 19 18
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18. Ex.: Ascending(ASC) or Descending(DESC) orders
SELECT Name, Major, Age
FROM STUDENT
WHERE GradeLevel IN ['FR', 'SO', 'SN']
ORDER BY Major ASC, Age DESC
BAKER
ACCOUNTING 41
PARKS
RYE 19 18
GLASS
HISTORY
JONES 50 24
ORDER BY can be combined with any of the SELECT statement
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19. 9.1.4 SQL Built-in Functions
Functions : COUNT, SUM, AVG, MAX, MIN
Ex.: count the number of STUDENT rows
SELECT COUNT (*)
FROM STUDENT 8
Ex.: count the number of DISTINCT Major
SELECT COUNT (Major)
FROM STUDENT
SELECT COUNT(DISTINCT Major) 8 3
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20. 9.1.5 Built-in Functions and Grouping
GROUP BY
Ex.: GROUP BY - count the number of students in each Major
SELECT Major, COUNT (*)
FROM STUDENT
GROUP BY Major
HISTORY 3
ACCOUNTING
MATH 2
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21. HAVING clause
Ex.: HAVING - groups of students having the same major are formed, and then groups having more than two students are selected
SELECT Major, COUNT (*)
FROM STUDENT
GROUP BY Major
HAVING COUNT(*) > 2
HISTORY 3
ACCOUNTING
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22. Ex.: HAVING and WHERE clause : WHERE condition is applied before or after the HAVING condition
SELECT Major, AVG (Age)
FROM STUDENT
WHERE GradeLevel = 'SN'
GROUP BY Major
HAVING COUNT(*) > 1
HISTORY 37
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23. 9.2 Querying Multiple Tables
2 Strategies
9.2.1 Retrieval Using Subquery
9.2.2 Joining with SQL
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24. 9.2.1 Retrieval Using Sub-Query
Ex.: need to know the names of those students enrolled in the class BD445
Step 1⇒ If we know that students with SIDs of 100 and 200 are enrolled in this class, then the following will produce the correct names
SELECT Name
FROM STUDENT
WHERE SID IN [100, 200]
Step 2⇒ can find SIDs of students in a class
SELECT StudentNumber
FROM ENROLLMENT
WHERE ClassName = 'BD445'
100
200
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25. Ex.: Combining the two queries, then can obtain the following
SELECT Name
FROM STUDENT
WHERE SID IN
(SELECT StudentNumber
FROM ENROLLMENT
WHERE ClassName = 'BD445')
-The second SELECT, which is called a subquery, is enclosed in parentheses
-SID and StudentNumber must come from the same domain
JONES
BAKER
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26. Step 2 ⇒need to identify number of students in these classes
Ex.: Subqueries can consists of three or even more tables we want to know the names of the students enrolled in classes in Monday, Wednesday, and Friday at 3 o’clock (MWF3)
Step 1 ⇒need the names of those classes that meet at MWF3
SELECT CLASS.Name
FROM CLASS
WHERE Time = 'MWF3'
Step 2 ⇒need to identify number of students in these classes
SELECT ENROLLMENT.StudentNumber
FROM ENROLLMENT
WHERE ENROLLMENT.ClassName IN
(SELECT CLASS.Name
WHERE Time = 'MWF3’)
100
200
300
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27. Ex.: Get the names of those students
SELECT STUDENT.Name
FROM STUDENT
WHERE STUDENT.SID IN
(SELECT ENROLLMENT.StudentNumber
FROM ENROLLMENT
WHERE ENROLLMENT.ClassName IN
(SELECT CLASS.Name
FROM CLASS
WHERE Time = 'MWF3'))
JONES
BAKER
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28. Problem in Subquery
Works well as long as the attributes in the answer come from a single table
If the result comes from two or more tables, we have a problem
Ex.: suppose we want to know the names of students and the names of their classes (for this, need SID, StudentName, ClassName)
In this case, the results come from two tables (STUDENT and ENROLLMENT), and so the subquery strategy will not work
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29. 9.2.2 Joining with SQL
Ex.: To produce the SID, StudentName, ClassName for every student, must join STUDENT table and ENROLLMENT table
SELECT STUDENT.SID, STUDENT.Name,
ENROLLMENT.ClassName
FROM STUDENT, ENROLLMENT
WHERE STUDENT.SID = ENROLLMENT.StudentNumber
100
150
200
300
400
450
JONES
PARKS
BAKER
RYE
BD445
BA200
CS250
CS150
BF410
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30. SELECT STUDENT.SID, ENROLLMENT.ClassName FROM STUDENT, ENROLLMENT
Ex.: WHERE clause can contain qualifiers in addition to those needed for the join
SELECT STUDENT.SID, ENROLLMENT.ClassName
FROM STUDENT, ENROLLMENT
WHERE STUDENT.SID = ENROLLMENT.StudentNumber
AND STUDENT.Name = 'RYE'
AND ENROLLMENT.PositionNumber = 1
400
BF410
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31. Ex.: Joining more than 2 tables
SELECT STUDENT.SID, CLASS.Name, CLASS.Time,
ENROLLMENT.PositionNumber
FROM STUDENT, ENROLLMENT, CLASS
WHERE STUDENT.SID = ENROLLMENT.StudentNumber
AND ENROLLMENT.ClassName = CLASS.Name
AND STUDENT.Name = 'BAKER'
200
300
BD445
MWF3
CS250
MWF12
CS150 2 1
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32. 9.2.3 Comparison of Join and Subquery
A join can be used as an alternative way of expressing many subqueries
Ex.: Finding the students enrolled in the class BD445
SELECT STUDENT.Name
FROM STUDENT, ENROLLMENT
WHERE STUDENT.SID = ENROLLMENT.StudentNumber
AND ENROLLMENT.ClassName = 'BD445’
Ex.: ”What are the names of the students in class MWF3
FROM STUDENT, ENROLLMENT, CLASS
AND ENROLLMENT.ClassName = CLASS.Name
AND CLASS.Time = 'MWF3'
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33. Comparison
1) Although join expressions can substitute for many subquery expressions, they cannot substitute for all of them(e.g. EXISTS and NOT EXISTS cannot be represented by joins)
2) subquery cannot be substituted for all joins as mentioned
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34. Ex.: we want to know the names of classes taken by undergraduates
1) Subquery
SELECT DISTINCT ClassName
FROM ENROLLMENT
WHERE StudentNumber IN
(SELECT SID
FROM STUDENT
WHERE GradeLevel NOT = 'GR')
2) Join
SELECT DISTINCT ENROLLMENT.ClassName
FROM ENROLLMENT, STUDENT
WHERE ENROLLMENT.StudentNumber =
STUDENT.SID AND
STUDENT.GradeLevel NOT = 'GR'
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35. Ex.: if we want to know both the names of the classes and the grade levels of the undergraduate students, must use a join (cannot use subquery)
SELECT DISTINCT ENROLLMENT.ClassName, STUDENT.GradeLevel
FROM ENROLLMENT, STUDENT
WHERE ENROLLMENT.StudentNumber = STUDENT.SID
AND STUDENT.GradeLevel NOT = 'GR'
BA200 SO
CS150 SN FR
BF410
CS250
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36. 9.2.4 Outer Join
ANSI standard SQL does not support outer joins. They are, however, supported by many DBMS products.
Suppose we want a list of all students and the names of the classes that they are taking. Further, suppose that we want to include all students, even those who are taking no class (the following SQL expression is given in MS Access)
SELECT Name, ClassName
FROM STUDENT LEFT JOIN ENROLLMETN
ON SID = StudentNumber;
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37. 9.2.4 Outer Join SELECT Name, ClassName
FROM STUDENT LEFT JOIN ENROLLMETN
ON SID = StudentNumber;
JONES
BD445
PARKS
BA200
BAKER
CS250
GLASS
null
CS150
RUSSELL
RYE
BF410
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38. 9.2.5 EXISTS and NOT EXISTS
EXISTS and NOT EXISTS: logical operators whose value is either true or false depending on the presence or absence of rows that fit the qualifying conditions
Ex.: EXISTS - we want to know the student numbers of students enrolled in more than one class
SELECT DISTINCT StudentNumber
FROM ENROLLMENT A
WHERE EXISTS
(SELECT *
FROM ENROLLMENT B
WHERE A.StudentNumber = B.StudentNumber
AND A.ClassName NOT = B.ClassName)
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39. 1) Find two rows in ENROLLMENT having the same student number but different class names. If two such rows exist, then the logical value of EXISTS is true
2) Imagine two separate and identical copies of the ENROLLMENT table (A and B). Compare each row in A and the first row in B. Then compare first row in A and the second row in B.
200
400
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40. NOT EXISTS
Ex.: we want to know the names of students taking all classes (wants the names of students such that there are no classes that the student did not take)
SELECT STUDENT.Name
FROM STUDENT
WHERE NOT EXISTS
(SELECT *
FROM ENROLLMENT
WHERE NOT EXISTS
(SELECT *
FROM CLASS
WHERE CLASS.Name = ENROLLMENT.ClassName
AND ENROLLMENT.StudentNumber = STUDENT.SID))
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41. 9.3 Changing Data 9.3.1 Inserting Data 9.3.2 Deleting Data
9.3.3 Modifying Data
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42. 9.3.1 Inserting Data Ex.: to insert a single row
INSERT INTO ENROLLMENT
VALUES (400, 'BD445', 44)
Ex.: If we do not know all of this data (attributes)
(if do not know PositionNumber)
(StudentNumber, ClassName)
VALUES (400, 'BD445')
Ex.: can copy rows in mass from one table to another.
INSERT INTO JUNIOR
VALUES
(SELECT SID, Name, Major
FROM STUDENT
WHERE GradeLevel = 'JR')
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43. 9.3.2 Deleting Data Ex.: deleting the row for Student 100
DELETE STUDENT
WHERE STUDENT.SID = 100
▶ If Student 100 is enrolled in classes, this delete will cause an integrity problem, as the ENROLLMENT rows having StudentNumber = 100 will have no corresponding STUDENT row.
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44. 9.3.2 Deleting Data
Ex.: Groups of rows can be deleted as shown in the next two examples (delete all enrollments for accounting majors as well as all accounting majors)
DELETE ENROLLMENT
WHERE ENROLLMENT.StudentNumber IN
(SELECT STUDENT.SID
FROM STUDENT
WHERE STUDENT.Major = 'ACCOUNTING')
DELETE STUDENT
WHERE STUDENT.Major = 'ACCOUNTING'
♠ The order of these two operations is important, for if it were reversed, non of the ENROLLMENT rows would be deleted because the matching STUDENT rows would already have been deleted
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45. 9.3.3 Modifying Data Ex.: UPDATE ENROLLMENT SET PositionNumber = 44
WHERE SID = 400
UPDATE ENROLLMENT
SET PositionNumber = MAX (PositionNumber) + 1
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46. Mass update (suppose the name of a course has been changed form BD445 to BD564. In this case, to prevent integrity problems, both the ENROLLMENT and the CLASS tables must be changed)
UPDATE ENROLLMENT
SET ClassName = 'BD564'
WHERE ClassName = 'BD445'
UPDATE CLASS
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