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# Cis245 Midterm Review

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### Transcript

• 1. CIS245
• 2.  Primary key Composite key/multiple-field primary key Foreign key One-to-one relationship One-to-many relationship Many-to-many relationship Referential Integrity
• 3.  Have more than one table where tables are related to each other  One to one  One to many  Many to manyA combination of fields may be used for the table‟s primary key
• 4.  Each table contains data about a specific subject (customers, loans) Each table on the „one‟ side has a primary key Primary key of the “one” table is a foreign key in the many table
• 5.  Twotables are related, but can have many records in each table in common  One student can attend many courses; one course can be attended by many students Implement a many to many relationship by creating a pair of one to many relationships with a third table  Third table is often referred to as a “join” or “junction” table
• 6. A foreign key points to a record in another table Foreign key “looks like” the related primary key  Same number of fields  Data types for each field must match  Field names don‟t matter
• 7.  Makessure that the records in related tables are consistent  Must have a customer in the customer table for an order assigned to that customer  Avoids “orphans” Cannotdelete a record or change the primary key in the one table when associated records are in the many table, unless have cascade delete and cascade update enabled
• 8.  Data constraints: What is “good” data?  Valid type of data  Valid values for the data  Many can be enforced through the design of the Access tables and relationships
• 9.  Validation rule: Condition that the corresponding field must satisfy Validation text: Displayed if the condition of validation rule is not satisfied Table Properties validation rule: Required when a constraint requires a comparison of the contents of two or more fields in the same table
• 10.  Maintains a sorted list of the current values of a field or fields Items in the list point to the records that have the identified value Created automatically for primary keys
• 11.  Normalization is a process Goals:  Reduce space required to store data by eliminating duplicate data in database  Reduce inconsistent data in database by storing data only once  Reduce chance anomalies
• 12.  Deletion anomaly  User deletes data from database  Unintentionally deletes only occurrence of data in database Update anomaly  Due to redundant data in database  User fails to update some records or updates records erroneously Insertion anomaly  User cannot add data to database unless preceded by entry of other data
• 13.  Dependency: Column value depends on value in a different column  Functional dependency: values explicitly one to one  Partial dependency: Column value dependent on only part of primary/candidate key
• 14.  Determinant: Field or collection of fields whose value determines value in another field Inverse of dependency  Department is a determinant
• 15.  Retrieve data from other tables or queries Field names appear in the Field row of the grid Criteria row of grid  Limits the displayed rows to those that meet a specified condition  Contains any statement that evaluates to True or False
• 16.  Inner join  Default join type  Includes rows only when the fields being compared contain matching values Outer join  Includes all rows from one table and data from second table where there is a match
• 17.  Use when selecting records from one table, but need to limit the records returned by a value in another table Use the „In‟ comparison  Sub-query can return only a single field Sub-query must run before the main query  Use parentheses to control order of execution
• 18.  Select queries that aggregate values The Group By item in the Total list box tells Access to aggregate the other fields per each unique value within the Group By field A field that‟s part of the aggregate uses Having instead of Where
• 19.  Delete queries: Remove rows from a table Make-table queries: Query results are stored in a new table Append queries: Query results of the are appended (added) to an existing Access table Update queries: Change field values in existing rows in a table
• 20.  Parameter queries use placeholder to substitute for the constant values placed in the query grid Allow changes to criteria “on the fly” when the query is run