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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
Difference between data warehouse and OLTP?
A data warehouse differs from OLTP in that the former handles many large and complex queries regarding various rows of a table while the latter retrieves data from single rows. At the same time, a data warehouse is not real time and supports few users at a time compared to OLTP that can support many concurrent users.
What is data manipulation language in rdbms?
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
- SELECT - retrieve data from the a database
- INSERT - insert data into a table
- UPDATE - updates existing data within a table
- DELETE - deletes all records from a table, the space for the records remain
- MERGE - UPSERT operation (insert or update)
- CALL - call a PL/SQL or Java subprogram
- EXPLAIN PLAN - explain access path to data
- LOCK TABLE - control concurrency
What are features of transaction processing system?
- Rapid Processing
- Reliability
- Standardisation
- Controlled Access
Where can you purchase reliable US Database?
Well last week I purchase Florida U.S database in Highleads.com and so far I'm happy with what i bought from them. They have different databases you can choose from and they accept paypal as a way of payment. I hope this will help you.
Reference http://www.highleads.com
What are the five main types of validation checks?
types of validations are: required field validation range validation pattern matching validation database specific validation numeric validation
Identify two limitations of physical models?
One limitation of a physical model is that a model of a human body may look like a human body, but does not act/work like a human body does.
( sorry only found one limitation )
What is the different between a view and a create view?
View is a virtual table that do not have any data of its own but have data that is derived from another table called base table. Create view is the command used to create a view (virtual table).
How do you change the length of a column in SQL?
The column definitions of a table can be modified using the ALTER TABLE command.
ALTER TABLE employee
MODIFY emp_name varchar2(100) not null;
This command makes the emp_name as a not null column and a alpha numeric column of 100 characeter width
Characteristics of relations in relational database model?
No Duplicate Tuples - A relation cannot contain two or more tuples which have the same values for all the attributes. i.e., In any relation, every row is unique.
• Tuples are unordered - The order of rows in a relation is immaterial.
• Attributes are unordered - The order of columns in a relation is immaterial.
• Attribute Values are Atomic - Each tuple contains exactly one value for each attribute.
It may be noted that many of the properties of relations follow the fact that the body of a relation is a mathematical set.
What is mean by strong entity?
A strong entity is any powerful force or presence, whether it is meant to mean some sort of deity, a high power such as a government or a business, or even an individual or group, etc.
What is DBA regarding database?
The DBA for a database is the Database Administrator. The DBA's roles are to manage the installation and configuration of the database software, to manage the allocation of space, to manage security, and (in concert with the developer) to manage data organization and query optimization. There are other roles, such as supporting backup and recovery, but this is just a small list.
Maximum number of subqueries you can write in SQL?
For practical matters there is no limit. However some DBMS, e.g. Sybase, have a limit of maximum 50 nesting levels and a maximum of 50 subqueries in each side of a union. However, for practical purposes is difficult to believe that there is a use for a query that involves 5o subqueries.
Jose D. Montero
Why databases important to a business?
When we maintain a small table of data, it could be easily accessed through MS Excel. However, this is not possible if we maintain large data as it simply takes much time to retrieve. when we maintain a large business data through a database using a tool like My SQL, we can add, update, delete or retrieve any data within seconds using a language like SQL. Also, we can link various databases for our convenience. Satheesh
A DBMS stores data in a table where the entries are filed under a specific category and are properly indexed. This allowed programmers to have a lot more structure when saving or retrieving data.
A relational database contains data in more than one table. Each table contains a database that is then linked to other tables with respect to their relationships.
Read more: Difference Between DBMS and RDMS | Difference Between | DBMS vs RDMS http://www.differencebetween.net/technology/difference-between-dbms-and-rdms/#ixzz1eJUZkRgz
How is indexing faster than sorting when accessing data from a table?
Indexing can be faster than sorting. It can also be slower. It depends on how many rows your predicate clause is selecting, and on the data dispersion represented by those index keys. If you are selecting a few rows, such as less than 4% of the table, then by all means use an index. If you are selecting a lot of rows, such as more than 25% of the table, then the use of the index will usually degrade performance, so go for the full table scan followed by a sort. (Of course, now you are adding the use of sort space, so that is a consideration.) The break-even point depends on the particular RDBMS and on the structure of the data. If your RDBMS supports EXPLAIN PLAN, then use it, and learn to know what it means. Also, make sure you understand your data, because (sometimes) only you know the best way to query it, and it might make sense to override the optimzer and force a certain execution plan based on your knowledge.
How do you enter data into the table?
You can enter data into a table using the INSERT keyword.
Ex:
INSERT INTO emp_master VALUES ('11111', 'john', '30, Newport pkwy, NJ')
The above command will insert one row of data into the emp_master table.
What is a one-to-many relationship?
It is a term from computer databases. A relational database can have a one-to-many relationship in its data. For example, if you have a customer order database, one table will contain customer names and another will contain their orders. Each customer will only be listed once, but each customer can make many orders. So one customer can be related to many orders. Incorporating that into a database requires the creation of a one to many relationship.
How do you build a database in visual foxpro?
On File choose New, a window will appear and ask you for New Project or Database. Choose Database and click New File. It will then ask you to give a database name. After your Database is made, you can now add tables.
What is the difference between data manipulation language and data definition language?
DDL or Data Definition Language is used to define the database and other related functions like creating tables, views, indexes etc. Some commands in DDL are:
- CREATE TABLE
- ALTER TABLE
- CREATE VIEW
- DROP TABLE
- etc.
DML or Data Manipulation Language is used to modify the contents of the data in a database. Ex:
- SELECT
- INSERT
- UPDATE
- DELETE
- ORDER BY
- GROUP BY
- etc.
DDL
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
- CREATE - to create objects in the database
- ALTER - alters the structure of the database
- DROP - delete objects from the database
- TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
- COMMENT - add comments to the data dictionary
- RENAME - rename an object
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
- SELECT - retrieve data from the a database
- INSERT - insert data into a table
- UPDATE - updates existing data within a table
- DELETE - deletes all records from a table, the space for the records remain
- MERGE - UPSERT operation (insert or update)
- CALL - call a PL/SQL or Java subprogram
- EXPLAIN PLAN - explain access path to data
- LOCK TABLE - control concurrency
SQL server is a database developed by the Microsoft corporation. The database is built to exclusively work on Microsoft Operating systems like Windows XP, Windows 2000, Windows Vista etc.
It works on all Windows based platforms, but it does depend on the Edition of SQL Server you are going to implement. For example you can run SQL Server Express on Windows Server, but you cannot run SQL Server Enterprise on Windows XP. It will only run on Windows Server systems.
Explain about primary key super key candidate key alternate key composite key foreign key?
KEYS IN SQL
* Alternate key - An alternate key is any candidate key which is not selected to be the primary key
* Candidate key - A candidate key is a field or combination of fields that can act as a primary key field for that table to uniquely identify each record in that table.
For Eg:
The table:
Emloyee(Name,Address,Ssn,Employee_Idprimary_key,Phone_ext)
In the above example Ssn no. and employee identity are ccandidate keys.
* Compound key - compound key (also called a composite key or concatenated key) is a key that consists of 2 or more attributes.
* Primary key - a primary key is a value that can be used to identify a unique row in a table. Attributes are associated with it. Examples of primary keys are Social Security numbers (associated to a specific person) or ISBNs (associated to a specific book).
In the relational model of data, a primary key is a candidate key chosen as the main method of uniquely identifying a tuple in a relation.
For Eg:
Emloyee(Name,Address,Ssn,Employee_Idprimary_key,Phone_ext)
* Superkey - A superkey is defined in the relational model as a set of attributes of a relation variable (relvar) for which it holds that in all relations assigned to that variable there are no two distinct tuples (rows) that have the same values for the attributes in this set. Equivalently a superkey can also be defined as a set of attributes of a relvar upon which all attributes of the relvar are functionally dependent.
For Eg:
Emloyee(Name,Address,Ssn,Employee_Idprimary_key,Phone_ext)
All the above are super keys.
* Foreign key - a foreign key (FK) is a field or group of fields in a database record that points to a key field or group of fields forming a key of another database record in some (usually different) table. Usually a foreign key in one table refers to the primary key (PK) of another table. This way references can be made to link information together and it is an essential part of database normalization.
For Eg:
For a Student....
School(Name,Address,Phone,School_Reg_noprimary_key
Why is accuracy data input important?
yes,data should b accurate in database.so that if any time we want to retrive data from database we will be able to see correct data.for example burger king arrange a special menu and pricing for weekends.and if data is not accurate then other branches of burger king will not get this information correctly.and due to this business can flop.
Data flow diagram for bus reservation system?
Data flow diagram of a bus reservation system will consists of pieces like customer , user screen, input , process , Output . These main entities will be interconnected by lines.
Difference between composite and primary key?
There are two types of keys in any database; composite and primary keys. Composite key differs from primary key in that it contains more than one column while primary key is composed of only one field and cannot have a null value.
