1. Getting to First Base: Introduction to Database Concepts
Chapter 14
Getting to First Base:
Introduction to Database Concepts

2. Tables: Special Kinds Of Lists
A database (DB) stores data
A relational database stores data in tables and describes the relationships among the different kinds of data
Databaspecifys are like the lists in spreadsheets, but with added constraints
Constraints limit the kinds of data they can contain, but expand the operations they can perform
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3. Entities
Anything that can de identified by a fixed number of its characteristics (attributes)
Attributes have names and values
The values are the data that's stored in the table
To create a table, we specify the entity's name (table name), the names of the entity's attributes, and the kinds of values each attribute can have
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4. Properties of Entities
Table Instances:
Table is initially empty. It has a name and column headings (the attribute names) but no rows
Each row will represent an entity
An instance of the database table is the table with a specific set of rows
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5. Properties Of Entities (Cont'd)
Structure: Content and Metadata
We separate the structure of the information from the information itself
A table's metadata includes its name, its attributes' names, the types of values each attribute can have, and the primary key, at a minimum
Some properties are not metadata: order of rows and columns is unimportant
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8. Properties Of Entities (cont'd)
Entities and Uniqueness
A database table doesn't have any duplicate rows
There must be at least one distinguishing characteristic to each entity
Some characteristics may be the same, but not all
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9. Properties Of Entities (cont'd)
Keys
Any set of attributes for which all attributes are different is a candidate key
Pick one and call it the primary key
Key must distinguish all potential and actual entities, not just those that happen to be in the table at a given times
If no combination of attributes qualify as a candidate key, assign a unique ID to each entity
Like a student ID number issued by school
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10. Operations on Tables Main use of database is to look up information
Users specify what they want to know, and the database finds it
Five fundamental operations that can be performed on tables: Select, Project, Union, Difference, Product
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11. Operations (cont'd) Select Operation
Takes rows from one table to create a new table
Specify the table from which rows are to be taken, and the test for selection
Syntax: Select Test From Table
Test is applied to each rows of the table to determine if it should be included in result table
Test uses attribute names, constants and relational operators
If the test is true for a given row, the row is included in the result table; otherwise it is ignored
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12. Operations (cont'd) Project Operation
Builds a new table from the columns of an existing table
Specify name of exiting table (or tables) and the columns (field names) to be included in the new table
Syntax:
Project Field_List From Table
The new table will have the number of columns specified, and the same number of rows as the original table, unless
The new table eliminates a key field. If rows duplicate in the new table, duplicates will be eliminated
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13. Operations (cont'd) Union Operation Difference Operation
Combines two tables (that have the same attributes)
Syntax:
Table1 + Table2
Difference Operation
Remove from one table the rows also listed in a second table
Table1 - Table2
Product Operation
Creates a super table with all fields from both tables
Puts the rows together
Table1 Table2
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14. Join Operation
Combines two tables, like the Product Operation, but doesn't necessarily produce all pairings
If the two tables each have fields with a common data type, new table combines only the rows from the given tables that match on the fields
Syntax:
Table1 Table2 On Match
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15. Join Operation (cont'd)
Match is a comparison test involving a field from each table
If the same field in table 1 contains the same data in the row for that field
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