Chapter 9 - Databases
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Database
Structured collection of data that allows people to extract information in a way that meets their needs
Single table database
Data base containing only one table
Table
Collection of related records in a database
Record
Collection of fields that describe one item (rows)
Field
Database table (columns)
How databases prevent problems (3)
Everyone uses the same data Data is consistent (changes/additions only have to be made once) Data only stored once in relational databases so no data duplication
What are data bases used for (3)
To store information about: -people -events -things
Difference between fields and records
Fields are fixed records can vary
Validation
Prevents incorrect data from being entered
Basic data types (6) in a database
Boolean Character Integer Text/alphanumeric Real Date/time
Data type
Classification of how data is stored and displayed and of which operations can be performed on the stored value
Primary key
Field in a database that uniquely identifies a record
SQL
Structured query language For writing scripts to obtain useful information from a relational database
SQL scripts
List of SQL commands that perform a given task often stored in a file so the script can be reused
FROM
SQL command that fetches specified fields (columns) from a table
WHERE
SQL command to include only those records in a query that match a given condition
ORDER BY
SQL command that sorts results from a query by a given column either alphabetically or numerically
SUM
SQL command that returns the sum of all values in a field (column) USED WITH SELECT
COUNT
SQL command that counts the number of records (rows) in which the field matches a specific condition Used with SELECT
SELECT
SQL command that fetches specified fields (columns) from a table