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Chapter ElevenData Manipulation Language (DML)
Nested QueriesDr. Chitsaz
Objectives• Nested queries
• Application of nested queries
• Conditions on nested queries
• Pair wise and non-pair wise comparison
• Union
• Minus
• intersection
2
SELECT ……
FROM …..
WHERE operator (SELECT ….
FROM ….);
Nested Queries:
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Rules:
• Inner query is executed first• Enclosed sub-queries in parentheses.• Sub-queries must be placed on the right side of the
comparison operator• Do not add an ORDER BY to a sub-query • Result is used by outer query• Sub-query can be placed in
WHEREHAVINGFROM
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Rules:
Operator:– Single row
= ,<>, > ,< , >= ,<=
– Multiple rowsANY IN ALL
• Use single row operators with a single row sub-query• Use multiple row operators with multiple rows
sub-query
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Example Data
SELECT * FROM Student;NAME ID MAJOR MINOR GPA------------------------------- ---- ---- ----------------James 243 COSC MATH 3.21John 102234 COSC MATH 3.32Sarah 201241 MATH COSC 3.20Mary 341235 MATH ENGL 2.11Walter 1111 ENGL MATH 1.41Sally 2001 MATH ENGL 3.00Isaac 201248 MATH COSC 4.00
7 rows selected.
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Example Data
SELECT * FROM Faculty;NAME ID SALARY DEPT AREA---------- ---------- -----------------------------------------------------Williams 191 34000 COSC DATA STRUCTURESJohnson 1234 30000 MATH CALCULUSJackson 413 45000 COSC NETWORKINGHook 103 25000 COSC DATABASEMorgan 127 32000 ENGL LITERATUREThomas 243 30000 MATH ALGEBRASmith 849 45000 COSC NETWORKINGAugustine 837 20000 COSC DATA STRUCTURES
8 rows selected.
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Example Data
SELECT * FROM Department;DEPARTMENT_NAME ID---- -----------------------------------------------ENGL 2003MATH 4513PSYC 1113COSC 2001MUSC 1233HIST 42513PHSC 4542CHEM 4113IDIS 3543
9 rows selected.
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Example Data
SELECT * FROM Student_course; ID C_NUM DEPT CREDITS NAME GRADE----------------------------------- ---------- ---- ---------- --------------
----------- 102234 360 MATH 3 MATH360 A 102234 100 MATH 3 MATH100 B 201241 310 COSC 3 COSC310 C 341235 250 COSC 3 COSC250 F 2001 120 ENGL 3 ENGL120 C 1111 360 ENGL 3 ENGL360 A 243 450 MATH 3 MATH450 B 2001 565 COSC 3 COSC565 C
8 rows selected.
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Nested Queries:
• Correlated sub-queries:
SELECT NameFROM Student WHERE GPA >
(SELECT GPA FROM Student WHERE ID= 243);
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Results
NAME
---------
John
Sarah
Isaac
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*Nested Queries*:
• Scalar sub-queries:
SELECT Name, IDFROM Student_course SORDER BY
(SELECT Department_Name
FROM Department D
WHERE S.id=D.id);
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Results
NAME ID--------------------------------------ENGL120 2001COSC565 2001MATH360 102234MATH100 102234ENGL360 1111MATH450 243COSC310 201241COSC250 341235
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Using group function in a sub-query:
• SELECT Name
FROM Faculty
WHERE Salary =(SELECT MIN(Salary )
FROM Faculty );
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Results
NAME
-------------
Augustine
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Using HAVING with sub-queries:
SELECT Dept, MIN(salary)
FROM Faculty
GROUP BY Dept
HAVING MIN(Salary) >
(SELECT MIN(Salary )
FROM Faculty
WHERE Dept='COSC');
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Results
DEPT MIN(SALARY)
------------------------------
ENGL 32000
MATH 30000
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Incorrect Statements:
SELECT Name
FROM Faculty
WHERE Salary =
(SELECT MIN(Salary )
FROM Faculty
GROUP BY Dept);
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No Value
SELECT Name
FROM Student
WHERE GPA =
(SELECT GPA
FROM Student
WHERE Name=‘NOHN');
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Multiple Row Sub-query:
• Name of students having Grade A:SELECT NameFROM Student WHERE ID IN
(SELECT ID FROM Student_Course
WHERE Grade='A' ); WHERE EXISTSWHERE NOT IN …. WHERE NOT EXISTS
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Results
NAME
-------
Walter
John
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Multiple Row Sub-query:
SELECT Name, IDFROM StudentWHERE ID IN
(SELECT ID FROM Faculty WHERE Dept IN
(SELECT Department_Name FROM Department WHERE ID = 2001) );
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Multiple Row Sub-query:
SELECT Name
FROM Student
WHERE GPA < ANY (SELECT GPA
FROM Student
WHERE Major='COSC' );
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Results
NAME
--------
James
Sarah
Mary
Walter
Sally
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*Multiple Row Sub-query*:
SELECT Name
FROM Student
WHERE ID > ALL
(SELECT ID FROM
Student_Course
WHEREMajor='COSC' );
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Results
NAME
--------
Sarah
Mary
Walter
Sally
Isaac
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Multiple Row Sub-query:
SELECT NameFROM FacultyWHERE Salary <
(SELECT Salary FROM Faculty
WHERE Faculty.ID =1234)
AND Dept =
(SELECT DeptFROM Faculty
WHEREArea='DATABASE');
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Results
NAME
------------
Hook
Augustine
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Multiple Row Sub-query:
• Name of Faculty who took courses
SELECT Name
FROM Faculty
WHERE EXISTS // IN (SELECT *
FROM Student_Course
WHERE Faculty.ID =
Student_Course.ID);
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Results
NAME
---------
Thomas
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Multiple Row Sub-query:
• Name of Faculty who did not take courses
SELECT Name
FROM Faculty
WHERE NOT EXISTS (SELECT *
FROM Student_Course
WHERE Faculty.ID =
Student_Course.ID);
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Results
NAME------------WilliamsJohnsonJacksonHookMorganSmithAugustine
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How to write this query?
– Find the department name and faculty name of the department with more than one faculty member.
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How to write this query?
– Find Departments with more than one Faculty
SELECT Dept, COUNT(*)FROM FacultyGROUP BY DeptHAVING COUNT(*) > 1;
Result: DEPT COUNT(*)
----------------------------COSC 5MATH 2
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How to write this query?
– Find department and name of faculty that are in each department with more than one faculty:
SELECT Dept, Name, COUNT(*)
FROM Faculty
GROUP BY Dept, Name
HAVING COUNT(*) > 1;
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How to write this query?
– SELECT Dept, Name
FROM Faculty a
WHERE EXISTS
(SELECT *
FROM Faculty b
WHERE a.Dept = b.Dept
GROUP BY b.Dept
HAVING COUNT(b.ID) > 1);
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Results
DEPT NAME--------------------------COSC Williams
MATH Johnson
COSC Jackson
COSC Hook
MATH Thomas
COSC Smith
COSC Augustine
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Multiple Column Sub-queries:
SELECT col1,col2, col3,…
FROM table
WHERE (col1,col2, ….) IN (SELECT (col1,col2,
….)
FROM table
WHERE condition );
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(Pair-wise Comparison)
• Name of students who have the same major and minor as Mary:
SELECT Name, ID, GPA
FROM Student
WHERE (major, minor) IN (SELECT Major, Minor
FROM Student
WHERE Name='MARY');
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Results
NAME ID GPA
---------- ---------------------------
Mary 341235 2.11
Sally 2001 3.00
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(Non-pair-wise Comparison)
SELECT Name, ID, SalaryFROM FacultyWHERE Salary IN
(SELECT SalaryFROM FacultyWHERE Dept='COSC') OR Area IN
(SELECT Area FROM Faculty
WHERE name =‘Williams');
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Results
NAME ID SALARY
-------------------------------------------------
Williams 191 34000
Jackson 413 45000
Hook 103 25000
Smith 849 45000
Augustine 837 20000
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Using a sub-query in the FROM clause
SELECT a.Dept, avgsalary
FROM Faculty a ,
(SELECT Dept , AVG(Salary) avgsalary FROM Faculty
GROUP BY Dept) b
WHERE a.Dept = b.Dept;
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Results
DEPT AVGSALARY----------------------------COSC 33800COSC 33800COSC 33800COSC 33800COSC 33800ENGL 32000MATH 30000MATH 30000
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Correlated Subquery
SELECT *
FROM Student
WHERE EXISTS (SELECT NULL
FROM Faculty
WHERE Faculty.Dept =
Student.Major);
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Results
NAME ID MAJOR MINOR GPA--------------------------------------------------------------------------
James 243 COSC MATH 3.21
John 102234 COSC MATH 3.32
Sarah 201241 MATH COSC 3.2
Mary 341235 MATH ENGL 2.11
Walter 1111 ENGL MATH 1.41
Sally 2001 MATH ENGL 3.0
Isaac 201248 MATH COSC 4.0
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SELECT ID
FROM Student
WHERE ID NOT IN
(SELECT ID
FROM Faculty
WHERE ID IS NOT NULL);
Note: If Faculty ID is nullable
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Results
ID----------
102234 201241 341235 1111 2001 201248
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Inline View
SELECT S.ID
FROM Student S, (SELECT IDFROM Faculty)
F
WHERE S.ID < > F.ID;
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Manipulating Data
• UNION:
List of students and faculty.
SELECT Name
FROM StudentUNION
SELECT Name
FROM Faculty;
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ResultsNAME------------AugustineHookIsaacJacksonJamesJohnJohnsonMaryMorganSallySarahSmithThomasWalterWilliams
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Manipulating Data
• UNION:
List of students and faculty.
SELECT Name
FROM StudentUNION ALL
SELECT Name
FROM Faculty;
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ResultsNAME----------JamesJohnSarahMaryWalterSallyIsaacWilliamsJohnsonJacksonHookMorganThomasSmithAugustine
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Manipulating Data
• INTERSECT:
List of students who are also a faculty member.
SELECT Name
FROM StudentINTERSECT
SELECT Name
FROM Faculty;
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Manipulating Data
• MINUS:
SELECT Name
FROM StudentMINUS
SELECT Name
FROM Faculty;
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Results
NAME-----------IsaacJamesJohnMarySallySarahWalter
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Question:
How many times will the subquery run?
SELECT a.ID, a.Name
FROM Student a
WHERE a.Major = (SELECT Name
From Department
---------------------);
DELETE FROM Student
WHERE ID = (SELECT MIN(ID)
FROM MyTable);
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Question:
How does this query proceed?
SELECT ID, Name, GPA, Major
FROM Student s
WHERE GPA = (SELECT MAX(GPA)
FROM Student
WHERE Major = s.Major);
58
Question:
Which query will run faster?
SELECT s.NameFROM Student sWHERE s.GPA = (SELECT MAX(GPA)
FROM Student);
SELECT *FROM (SELECT s.Name, GPA,
DENSE_RANK OVER (ORDER BY GPA DESC) d
FROM Student s)WHERE d = 1;
