0
Database Programming
Databases are collections of tables that maintain and display information, often collaboratively; this information can be used for interaction with an application or gaining general knowledge. Questions about database engines and modifying or using them belong in this category.
8,803 Questions
What is a table and what role does it play in the relational model?
A table is a matrix of intersecting rows and columns. In the relational model, the table view of data makes it easy to spot and define entity relationships, thereby greatly simplifying the task of database design.
Is the DMV database connected with all states?
No, the DMV database is not connected across all states. Each state typically maintains its own DMV database, although some states may participate in data-sharing agreements to exchange certain information.
What are the advantages of patriachar social system?
Some people believe that the advantages of a patriarchal social system include clear gender roles, stability in family structures, and a sense of tradition and continuity. However, it is important to note that this system can also lead to inequality, limited opportunities for women, and perpetuation of harmful gender stereotypes.
What is the function of a Foreign Key in SQL?
A Foreign Key in SQL is used to establish a relationship between two tables. It ensures referential integrity by enforcing that values in a column (or columns) in one table must match the values in a primary key in another table. This helps maintain consistency and data integrity across linked tables.
A relationship between the instances of a single entity type is called a ........................?
A relationship between instances of a single entity type is called a self-relationship or recursive relationship. This type of relationship occurs when an entity is related to other instances of the same entity type within the same entity set.
Is a query language a procedural language?
No, a query language is not a procedural language. Query languages are used to retrieve specific information from databases or other data sources by defining and executing queries, while procedural languages are used to write algorithms and executable instructions to solve problems.
A foreign key is a column or a set of columns in one table that references the primary key in another table, creating a relationship between the two. This relationship ensures data integrity by enforcing referential integrity constraints, allowing for the proper establishment of connections between related data in a database. It helps maintain data consistency by preventing actions that would create orphaned records or violate the defined relationship between the tables.
An unsafe query is a query that is vulnerable to SQL injection, allowing malicious users to run unauthorized commands on a database. Example: "SELECT * FROM users WHERE username = 'admin' AND password = 'password' OR 1=1;". It's crucial to disallow such queries to prevent security breaches, data manipulation, unauthorized access to information, and potential damage to the database.
List out Codd's rules for Relational Databases?
Rule 1: The information rule:All information in the database is to be represented in one and only one way, namely by values in column positions within rows of tables.
Rule 2: The guaranteed access rule:All data must be accessible. This rule is essentially a restatement of the fundamental requirement for primary keys. It says that every individual scalar value in the database must be logically addressable by specifying the name of the containing table, the name of the containing column and the primary key value of the containing row.
Rule 3: Systematic treatment of null values:The DBMS must allow each field to remain null (or empty). Specifically, it must support a representation of "missing information and inapplicable information" that is systematic, distinct from all regular values (for example, "distinct from zero or any other number", in the case of numeric values), and independent of data type. It is also implied that such representations must be manipulated by the DBMS in a systematic way.
Rule 4: Active online catalog based on the relational model:The system must support an online, inline, relational catalog that is accessible to authorized users by means of their regular query language. That is, users must be able to access the database's structure (catalog) using the same query language that they use to access the database's data.
Rule 5: The comprehensive data sublanguage rule:The system must support at least one relational language that
- Has a linear syntax
- Can be used both interactively and within application programs,
- Supports data definition operations (including view definitions), data manipulation operations (update as well as retrieval), security and integrity constraints, and transaction management operations (begin, commit, and rollback).
Rule 6: The view updating rule:All views that are theoretically updatable must be updatable by the system.
Rule 7: High-level insert, update, and delete:The system must support set-at-a-time insert, update, and delete operators. This means that data can be retrieved from a relational database in sets constructed of data from multiple rows and/or multiple tables. This rule states that insert, update, and delete operations should be supported for any retrievable set rather than just for a single row in a single table.
Rule 8: Physical data independence:Changes to the physical level (how the data is stored, whether in arrays or linked lists etc.) must not require a change to an application based on the structure.
Rule 9: Logical data independence:Changes to the logical level (tables, columns, rows, and so on) must not require a change to an application based on the structure. Logical data independence is more difficult to achieve than physical data independence.
Rule 10: Integrity independence:Integrity constraints must be specified separately from application programs and stored in the catalog. It must be possible to change such constraints as and when appropriate without unnecessarily affecting existing applications.
Rule 11: Distribution independence:The distribution of portions of the database to various locations should be invisible to users of the database. Existing applications should continue to operate successfully :
- when a distributed version of the DBMS is first introduced; and
- when existing distributed data are redistributed around the system.
Rule 12: The nonsubversion rule:If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to subvert the system, for example, bypassing a relational security or integrity constraint.
What statement is used to execute a procedure?
Just use the name of the procedure.
For example, if I have a procedure addEntry(a NUMBER, b OUT NUMBER) then I can call it by:
DECLARE
x NUMBER;
BEGIN
addEntry(5, x);
END
.
run;
What are the risks of a national DNA database?
Some potential risks of a national DNA database include concerns about privacy and data security, as well as the potential for misuse of genetic information by governments or other entities. There are also ethical considerations related to consent and the potential for discrimination based on genetic information.
What SQL clause is used to restrict the rows returned by a query?
The WHERE clause is used to restrict the rows returned by a query in SQL. It allows you to specify a condition that must be met for a row to be included in the result set.
Explain how validation rules can help maintain The integrity of a database?
Validation rules help maintain the integrity of a database by enforcing data accuracy and consistency. They ensure that only valid data entries are allowed, preventing errors such as incorrect data types, values out of range, or missing values. This helps in maintaining data quality and reliability within the database.
Explain various DDl commands in SQL?
DDL (Data Definition Language) commands in SQL are used to define the structure of database objects. Some common DDL commands include:
- CREATE: Used to create database objects like tables, views, indexes, etc.
- ALTER: Used to modify the structure of existing database objects.
- DROP: Used to delete database objects.
- TRUNCATE: Used to delete all records from a table.
Explain the differences between the Rhode Island system and the Lowell system?
Rhode Island System: Samuel Slater's strategy of hiring families and dividing factory work into simple tasks
Lowell system: based on water-powered textile mills that employed young, unmarried women from local farms; included a loom that could both spin thread and weave cloth in the same mill
What does circling the stomach in sign language mean?
In American Sign Language, circling the stomach is a gesture commonly used to refer to hunger or having stomach pain. It can indicate a general feeling of discomfort or being unwell in the stomach area.
What does a bacwards wave mean in sign language?
I believe you are referring to "in the past" or "long ago." The more waves you make, the further in the relative past it is. One wave is very recent, like a few days. Many waves goes back years, even centuries. It's not precise, just a description.
What is a field that is chosen to uniquely identify a record called?
A field that is chosen to uniquely identify a record is called a primary key. This key helps uniquely identify each record in a database table and ensure data integrity.
Is SQL a database or language?
SQL is a language used to communicate with databases. It stands for Structured Query Language. It is used to perform tasks such as querying data, updating data, creating databases, and managing databases.
In HyperMesh, skew is a measure of the quality of the elements. It calculates the deviation of the shape of an element from an ideal shape (usually a square or a cube). Lower skew values indicate better element quality, while higher skew values indicate distorted elements that may negatively impact analysis results. It is important to address and minimize skew to ensure accurate and reliable simulation results.
What are the Properties of relational database model?
The relational database model organizes data into relations or tables with rows and columns, providing a clear structure for data storage. It supports the concept of primary keys to uniquely identify each record in a table and foreign keys to establish relationships between tables. Additionally, it ensures data integrity through constraints like referential integrity and data normalization.
List the different types of database user and explain?
4 Types of Database Users Users are differentiated by the way they expect to interact with the system: · Application programmers - interact with system through DML calls. · Sophisticated users - form requests in a database query language. · Specialized users - write specialized database applications that do not fit into the traditional data processing framework. · Naive users - invoke one of the permanent application programs that have been written previously.
FROM: Database Systems Concepts 1.17 Silberschatz, Korth and Sudarshan c1997
Codd's twelve rules are a set of thirteen rules (numbered zero to twelve) proposed by Edgar F. Codd, a pioneer of the relational model fordatabases, designed to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system (RDBMS).[1][2] They are sometimes jokingly referred to as "Codd's Twelve Commandments".
The relational DBMS model is based on the relational algebra devised by E.F.CODD.
The relational algebra by Codd is done through 12 rules popularly known as CODD's 12 Rules.
(1)Information Rule:
All information in a relational database including table names column names are
represented explicitly by values in tables.Knowledge of only one language is necessary to
access all data such as description of the table and attribute definitions integrity
constraints action to be taken when constraints are voilated and security information.
(2)Guaranted Access Rule:
Every pieceof data in the relational database can be accessed by using a
combination of a table name a primary key value that identifies the row and a column
that identifies the cell.The benefit of this is that user productivity is improved
since there is no need to resort to using physical pointers addresses.Provides
data independence.
(3)Systematic treatment of Nulls Rule:
The RDBMS handles that have unknown on inapplicable values in a predefined fashion.
RDBMS distinguishes between zeros blanks and nulls in records and handles such values in
a consistent manner that produces correct answers comparisions and calculations.
(4)Active On-Line Catalog Based on the Relational Model.
THe description of a database and its contents are database tables and therefore
can be queries online via the data language.The DBA's productivity is improved since
changes and additionsto the catalog can be done with the same commands that are
used to access any other table.All queries and reports can be done as with other tables.
(5)Comprehensive Data Sublanguage Rule:
A RDBMS may support several languages but atleast one of them allows the user to do all
of the following:define tables view query and update data set integrity constraints
set authorization and define transactions.
(6)View Updating Rule:
Any view that is theoretically updatable if changes can be made to the tables that
effect the desired changes in the view.Data consistency is ensured since changes
in the underlying tables are transmittedto the view they support.Logical data
independence reduces maintenance cost.
(7)High Level Inserts Update and Delete:
THe RDBMS supports insertion updation and deletion at a table level.With this the
RDBMS can improveperformance by optimizing the path to be taken to execute the action
Ease of use improved since commands act on set of records.
(8)Physical data Independence :
The execution of adhoc requests and application programs is not affected by changes
in the physical data access and storage methods.Database administrators can make
the changes to physical acccess and storage methods which improve performance
but do not changes in the application programs or adhoc requests.This reduces
maintenance costs.
(9)Logical data Independence:
Logical changes in tables and view such asadding/deleting columns or changing
field lenghts do not necessitate modifications in application programs or in the
format of adhoc requests.
(10)Integrity Independance:
Like table/view definitions integrity constraints are atored in the
on-line catalog and therefore can be changed without necessitating changes
in application programs or in the format of adhoc requests .
The following two integrity constraints must be supported.
(a)Entity Integrity:
No component of primary key is allowed to have anull value.
(b)Referential integrity:
For each distinct non-null foreign key value in a relationaldatabase
there must exist a matching primary key from the same range of data value.
(11)Distribution Independence:
Application programs and adhoc requests are not affected by changes
in the distribution of the physical data.
(12)Nonsubversion Rule:
If the RDBMS has a language change that accesses the information
of a record at a time this language cannot be used to by-pass the
integrity constraints.Inoreder to adhere to this rule the RDBMS must have an
active catalog that containsthe constraints must have a logical data independence.
