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DBMS IT2043
Ch. 4 Data Queries
16
Computer Science
Undergraduate 2
12/08/2010

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Cards

Term
aggregation
Definition
Computations of totals and subtotals...
examples: Sum, AVG, Min, Max, Count, StDev, StdDev, Var
Term
alias
Definition
giving table a new name - useful when needing data from one table for two entities ( customer city and employee city both stored in city table)
Term
What are the three basic tasks of a query language?
Definition
1. Define the Database
2. Change the data
3. Retrieve the data
Term
What are the four questions used to create a query?
Definition
(1)SELECT - What output (columns and calculations) do you want to see?
(2)FROM - What do you know or what constraints are given?
(3)JOIN - What tables are involved?
(4)WHERE - How are the tables joined? What needs to be met?
Term
What is the basic structure of the SQL SELECT command?
Definition
SELECT columns or SELECT Table.Column
Term
What is the purpose of the DISTINCT operator?
Definition
Tells the DBMS to display only rows that are unique
Term
Why is it important to use parentheses in complex (Boolean) WHERE clauses?
Definition
Term
How is pattern matching used to select rows of data?
Definition
p. 191 it allows you to search for data that is matches a pattern using wildcards for all data before or for a singel
Term
What is DeMorgan’s law, and how does it simplify conditions?
Definition
Term
How do you compute subtotals using SQL?
Definition
Term
How do the basic SQL arithmetic operators (+, -, etc.) differ from the aggregation (SUM, etc.) commands?
Definition
Term
What basic aggregation functions are available in the SELECT command?
Definition
Term
What is the difference between Count and Sum? Give an example of how each would be used.
Definition
Term
What is the difference between the WHERE and HAVING clauses? Give an example of how each would be used.
Definition
Term
What is the SQL syntax for joining two tables?
Definition
Term
How do you identify a column when the same name appears in more than one table?
Definition
table.column
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