Introduction to Database Systems Queries in SQL The select ...

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Nested Queries: Comments • The nested formulation of a query is usually executed less efficiently than an equivalent unnested formulation (due to limitations of the query optimizer). • The nested formulation is sometimes more readable. • The subqueries cannot contain set operators (“union is only performed at the top level”), but this is not a significant limitation. 75 Nested Queries: Example with all “Persons who have an income that is higher than the income of all persons younger than 30” 76
Nested Queries: Example with all “Persons who have an income that is higher than the income of all persons younger than 30” select name from person where income >= all (select income from person where age < 30) 77 Equivalent Formulation with max “Persons who have an income that is higher than the income of all persons younger than 30” select name from person where income >= (select max(income) from person where age < 30) 78
Page 1 and 2: Introduction to Database Systems Qu
Page 3 and 4: Naming Conventions • To avoid amb
Page 5 and 6: Usage of “as” in select Stateme
Page 7 and 8: select with Asterisk Given a relati
Page 9 and 10: Handling of Null Values Employees w
Page 11 and 12: SQL and Relational Algebra Given th
Page 13 and 14: MotherChild mother child Lisa Mary
Page 15 and 16: Exercise 4: Solution “Father and
Page 17 and 18: Explicit Join For every person, ret
Page 19 and 20: A Further Extension: Natural Join (
Page 21 and 22: Ordering the Result: order by selec
Page 23 and 24: Results of count: Example FatherChi
Page 25 and 26: Aggregate Operators and the Target
Page 27 and 28: Exercise 7: group by “For each gr
Page 29 and 30: Conditions on Groups It is also pos
Page 31 and 32: Union, Intersection, and Difference
Page 33 and 34: Positional Notation (cntd) Renaming
Page 35 and 36: Single Block Queries: Exercises (cn
Page 37: Nested Queries: Example Name and in
Page 41 and 42: Nested Queries and Negation All the
Page 43 and 44: Exercise 9: Solution with not exist
Page 45 and 46: More on Visibility Note: This query
Page 47 and 48: Exercise 10: Solution “Name and a
Page 49 and 50: Exercise 11 Can one express set dif
Page 51 and 52: Exercise 12: Solution “The person
Page 53 and 54: Solution with Views create view age
Page 55 and 56: Generic Integrity Constraints: chec
Page 57 and 58: Characteristics of Privileges A pri
Page 59 and 60: Example Transaction in SQL begin tr
Page 61 and 62: Transactions • A transaction is a
Page 63 and 64: Transactions are … Durable • Af
Page 65 and 66: Integrity Checking and Transactions
Page 67 and 68: Concurrency Control • There are t
Page 69 and 70: Isolation Levels Prevent Violations
Page 71 and 72: Transactions (Example ctd) Lubber a

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