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20 Cards in this Set
- Front
- Back
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What is cardinality? |
Thinking mathematically, it is the number of elements in a set. Thinking in the database world, cardinality has to do with the counts in a relationship, one-to-one, one-to-many, or many-to-many. |
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Describe the differences in the first normalization forms. |
The domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain. |
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Describe the differences in the second normalization forms. |
No non-prime attribute in the table is functionally dependent on a proper subset of any candidate key.Third: Fourth:.Fifth: . |
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Describe the differences in the third normalization forms. |
Every non-prime attribute is non-transitively dependent on every candidate key in the table. The attributes that do not contribute to the description of the primary key are removed from the table. In other words, no transitive dependency is allowed. |
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Describe the differences in the fourth normalization forms. |
Every non-trivial multivalued dependency in the table is a dependency on a superkey |
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Describe the differences in the fifth normalization forms. |
Every non-trivial join dependency in the table is implied by the superkeys of the table |
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When might someone denormalize their data? |
Typically done for performance reasons, to reduce the number of table joins. This is not a good idea in a transactional environment as there are inherent data integrity risks or performance risks due to excessive locking to maintain data integrity. |
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What are the elements of an ERD? |
The three elements include the entities for which someone is seeking information, the attributes of those entities, and the relationships between the entities. |
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Which SQL command is used to add a row? |
INSERT |
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Write the command to remove all employees named John from the EMPLOYEE table. |
DELETE from EMPLOYEE WHERE firstName = ‘John’ |
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What does SQL stand for? |
Structured Query Language |
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What are the differences between primary and foreign keys? |
The primary key is the column or set of columns used to uniquely identify the items in a table. A foreign key is used to uniquely identify the items in a different table, allowing join operations to happen.
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What is the difference between an inner and outer join? |
An inner join involves joining two tables where a common id/key exists in both. An outer join is the joining of two tables, but where there is no match in the second (or first). |
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How do you maintain database integrity where deletions from one table will automatically cause deletions in another table? |
You create a trigger that will automatically delete elements in the second table when elements from the first table are removed. |
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What port does SQL server run on? |
1433 is the standard port for SQL server. |
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What is the SQL CASE statement used for and give an example? |
It allows you to embed an if-else like clause in the SELECT clause. |
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What are Hadoop and Hive? |
Hadoop is an Apache project for dealing with large data sets, basically providing a file system with libraries for large scale data processing like map-reduce. Hive provides the layer on top of Hadoop for query and analysis. The query language is calle HiveQL and does not support transactions. |
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What is Hibernate? |
Hibernate is an object-relational mapping library that takes Java objects and maps them into relational database tables. It provides its own query language (Hibernate Query Language / HQL) that fills in where SQL falls short when dealing with objects. The latest version as of June 2014 is 4.3.5. |
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What is NoSQL? |
It stands for Not Only SQL and provides an alternative to relational databases. Instead of tabular data stores, they use graph stores, key-value stores, document databases, and wide-column stores. It is popular in the agile development world as developers don’t have to finalize the data model before storing information. |
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What are the risks of storing a hibernate-managed object in a cache? And, how do you overcome the problems? |
With an answer of something along the lines of the following; The primary problem here is the object will outlive the session it came from. Lazily loaded properties won’t get loaded if needed later. To overcome the problem, cache just the object’s id and class, then have retrieve the object in the current session context. |
