Trouble Spots Flashcards
SELECT (RESTRICT) yields a horizontal subset of a single table.
True
PROJECT yields a vertical subset of a single table.
True
UNION combines all rows from two tables excluding duplicate rows. The columns and domains of the two tables must be compatible.
True
INTERSECT yields only the rows that appear in both tables. Tables must be union-compatible.
True
DIFFERENCE yields all rows in one table that are not found in the other; that is it subtracts one table from another. Tables must be union-compatible.
True
PRODUCT yields all possible pairs of rows from two tables.
True
NATURAL JOIN links tables by selecting only the rows with common values in their common attributes.
True
INNER JOIN only returns matched records from the tables being joined.
True
OUTER JOIN returns the matched pairs of the inner join plus the unmatched records from one of the tables.
True
LEFT OUTER JOIN yields all the rows in the left table including those that have no matching values in the other table
True
RIGHT OUTER JOIN yields all the rows in the right table including those that have no matching values in the other table
True
DIVIDE is used to answer questions about one set of data being associated with all values in another set. DIVIDE uses one double-column table as the dividend and one single-column table as the divisor.
True
All information in a relational database must be logically represented as column values in rows within tables.
Information; Rule 1
Every value in a table is guaranteed to be accessible through a combination of table name, primary key value, and column name.
Guaranteed access; Rule 2
Nulls must be represented and treated in a systematic way, independent of data type.
Systematic treatment of nulls; Rule 3
The metadata must be stored and managed as ordinary data - that is, in tables within the database; such data must be available to authorized users using the standard database relational language.
Dynamic online catalog based on the relational model; Rule 4
The relational database may support many languages; however it must support one well-defined, declarative language as well as data definition, view definition, data manipulation (interactive and by program), integrity constraints, authorization, and transaction management (begin, commit, and rollback).
Comprehensive data sublanguage; Rule 5
Any view that is theoretically updatable must be updatable through the system.
View updating; Rule 6
The database must support set-level inserts, updates, and deletes.
High-level insert, update, and delete; Rule 7
Application programs and ad-hoc facilities are logically unaffected when physical access methods or storage structures are changed.
Physical data independence; Rule 8
Application programs and ad-hoc facilities are logically unaffected when changes are made to the table structures that preserve the original table values (changing order of columns or inserting columns).
Logical data independence; Rule 9
All relational integrity constraints must be definable to the relational language and stored in the system catalog (not at the application level).
Integrity independence; Rule 10
If the system supports low-level access to the data, users must not be allowed to bypass the integrity rules of the database.
Non-subversion; Rule 12
The end users and application programs are unaware of and unaffected by the data location (distributed vs. local databases).
Distribution independence; Rule 11
All proceeding rules are based on the notion that to be considered relational, a database must use its relational facilities exclusively for management.
Rule 0
