Zusammenfassung der Ressource
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Characteristics for the hierarchical structure:
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A subordinate can be reached in many ways
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A subordinate node can have only one superior
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A node can have any number of subordinates and superiors
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A subordinate node must have many superiors
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A superior may have one or many subordinates
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In a table one can have:
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A simple primary key
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A composed primary key
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A simple foreign key
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A foreign primary key
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A control key
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The conceptual schema is the result of:
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The system study
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The system analysis
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The application requirements
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The database structure's design
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The database functions' design
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The clusters are useful for:
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Optimizing the database
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Requests
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Updates
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Data inserts
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Documentary databases
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A components database system architecture includes:
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Having the table STUDENT ( name, year, group, no_stud_group, group_secretary, birth_date), what affirmation(s) is(are) not true:
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The table is in 2NF
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The table has a fully functionally dependence
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The table has a non-transitive dependence
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The table is normalized
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The table has a composed primary key
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In the relational model:
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There is the "record" notion
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The attributes that have a role in making the links between tables are called composed keys
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The links between tables are described in DML
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There is the "table schema" notion
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Projection, negation and existential are relational algebra operators
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Having the tables
PRODUCTS (product_id NUMBER(15) primary key, name VARCHAR2(25), price NUMBER (7, 2), release_date DATE),
ORDERS (order_id NUMBER(10) primary key, product_id NUMBER (15) REFERENCES products(product_id), quantity NUMBER(7,2), order_date DATE).
Select the orders that were made for the products that were released in 2000 (in two ways)
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select o.order_id, p.name, p.release_date, o.quantity from products p, orders o where p.product_id = o.product_id and extract (year from p.release_date) = 2000;
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select o.order_id, p.name, p.release_date, o.quantity from products p join orders o using(product_id) where to_char(p.release_date, 'DD.MM.YYYY') like '%2000';