1. SQL : Query Language
Part II
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2. Sorting: ORDER BY clause
SELECT *
FROM Student
WHERE sNumber >= 1
ORDER BY sNumber, sName
 (sNumber, sName) ( (sNumber >= 1) (Student))
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3. Subqueries Subquery returns a relation
Nest subqueries into WHERE clause
Nest subqueries into FROM clause
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4. Subqueries SELECT * FROM Student WHERE professor = (SELECT pName
FROM Professor
WHERE pNumber=1)
Note: The inner subquery returns a relation, but SQL runtime ensures that subquery returns a relation with one column and with one row, otherwise it is a run-time error.
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5. Subqueries - Example Student SELECT * FROM Student WHERE professor =
(SELECT pName
FROM Professor
WHERE pNumber=1)
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
Professor
pNumber
pName
address 1 MM
141FL 2 ER
201FL
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg
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6. Subqueries We can use IN, EXISTS, NOT IN, and NOT EXISTS
ALL, ANY can be used with comparisons
SELECT * FROM Student
WHERE (sNumber, professor) IN
(SELECT pNumber, pName
FROM Professor)
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7. Subqueries - Example Student Professor SELECT * FROM Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
pNumber
pName
address 1 MM
141FL 2 ER
201FL
SELECT * FROM Student
WHERE (sNumber, professor) IN
(SELECT pNumber, pName
FROM Professor)
sNumber
sName
address
professor 1
Dave
320FL MM
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8. Subqueries: EXISTS Professor Student SELECT * FROM Student
WHERE EXISTS
(SELECT pName FROM Professor
WHERE Student.professor=pName)
Professor
pNumber
pName
address 1 MM
141FL 2 ER
201FL
Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
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9. Subqueries with negation
SELECT * FROM Student
WHERE (sNumber, professor) NOT IN
(SELECT pNumber, pName
FROM Professor)
Professor
pNumber
pName
address 1 MM
141FL 2 ER
201FL
Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
sNumber
sName
address
professor 2
Greg
320FL MM 3
Matt ER
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10. Subqueries with negation
Student
Professor
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
pNumber
pName
address 1 MM
141FL 2 ER
201FL
SELECT * FROM Student
WHERE NOT EXISTS
(SELECT pName FROM Professor
WHERE Student.professor=pName)
sNumber
sName
address
professor
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11. Subqueries: ALL, ANY
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12. Subqueries: ALL - Example
Student
Professor
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
pNumber
pName
address 1 MM
141FL 2 ER
201FL
SELECT * FROM Student
WHERE sNumber > ALL
(SELECT pNumber
FROM Professor)
sNumber
sName
address
professor 3
Matt
320FL ER
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13. Subqueries: ANY - Example
Student
Professor
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
pNumber
pName
address 1 MM
141FL 2 ER
201FL
SELECT * FROM Student
WHERE sNumber = ANY
(SELECT pNumber
FROM Professor)
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg
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14. Subqueries: NOT ALL - Example
Student
Professor
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
pNumber
pName
address 1 MM
141FL 2 ER
201FL
SELECT * FROM Student
WHERE NOT sNumber > ALL
(SELECT pNumber
FROM Professor)
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg
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15. Subqueries: NOT ANY - Example
Student
Professor
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
pNumber
pName
address 1 MM
141FL 2 ER
201FL
SELECT * FROM Student
WHERE NOT sNumber = ANY
(SELECT pNumber
FROM Professor)
sNumber
sName
address
professor 3
Matt
320FL ER
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16. Subqueries: Correlation
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17. Subqueries in FROM clause
SELECT sName, pName
FROM Student,
(SELECT * FROM Professor
WHERE pNumber=1)
WHERE professor=pName;
Professor
pNumber
pName
address 1 MM
141FL 2 ER
201FL
Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
sName
pName
Dave MM
Greg
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18. Duplicate Elimination
SELECT DISTINCT address
FROM Student
WHERE sNumber >= 1;
SELECT DISTINCT *
FROM Student;
(Student)
( (address) ( (sNumber >= 1) (Student)))
Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
address
320FL
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19. Aggregation + GroupBy
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20. Aggregation Functions
SELECT COUNT (*) FROM Student;
SELECT COUNT (sNumber) FROM Student;
SELECT MIN (sNumber) FROM Student;
SELECT MAX (sNumber) FROM Student;
SELECT SUM (sNumber) FROM Student;
SELECT AVG (sNumber) FROM Student;
We can have distinct such as:
SELECT COUNT (DISTINCT sNumber) FROM Student
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21. Grouping
SELECT COUNT (sName) as cnum
FROM Student
GROUP BY address;
(COUNT (sName) as snum) ( (address, COUNT (sName)) (Student))
Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER
COUNT (sName) 3
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22. Grouping SELECT address, COUNT (sNumber) FROM Student
WHERE sNumber > 1
GROUP BY address
HAVING COUNT (sNumber) > 1;
Student
sNumber
sName
address
professor 1
Dave
320FL MM 2
Greg 3
Matt ER 4
Ben
300FL
address
COUNT (sNumber)
320FL 2
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23. Aggregation and NULLs
NULLs are ignored in any aggregation; except COUNT (*)
However if the set of attributes to be grouped on has null values, then grouping is done on the null values as well.
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24. SQL Queries - Summary SELECT [DISTINCT] a1, a2, …, an
FROM R1, R2, …, Rm
[WHERE C1]
[GROUP BY g1, g2, …, gl [HAVING C2]]
[ORDER BY o1, o2, …, oj]
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