- The Primary key constraint uniquely identifies each record in a database table.
- Primary keys must contain unique values.
- A primary key column cannot contain Null values.
- Each table should have a primary key, and each table can have only One primary key.
Friday 17 February 2012
What is a Primary Key ?
Thursday 2 February 2012
Definition of Database?, What is Data Base Management System(DBMS)?
Database:-
A database is a collection of information that is organized so that it can easily be accessed, managed, and updated.There are different types of database but the most popular is a relational database that stores data in tables where each row in the table holds the same sort of information.
Data Base Management System(DBMS):-
Data Base Management System(DBMS):-
A database management system (DBMS) is the software that allows a computer to perform database functions of storing, retrieving, adding, deleting and modifying data. Relational database management systems (RDBMS) implement the relational model of tables and relationships.
Database Applications:-
1.Computerized library systems automated teller machines
2.Flight reservation systems
3.Storage and reproduction of graphics images,video and audio
4.Online reservations
1.what is meant by a Database?
a)Collection of interrelated data or tables is as database.
2.what is the use of Database?
a) It is used to store the data in the table form.
3.what is meant by a table?
a)collection of records or a table is a set of data elements (values) that is organized using a model of vertical columns(which are identified by their name) and horizontal rows. A table has a specified number of columns, but can have any number of rows. Each row is identified by the values appearing in a particular column subset which has been identified as a candidate key.
(or)
A single store of related information. A table consists of records, and each record is made up of a number of fields. Just to totally confuse things, tables are sometimes called relations. You can think of the phone book as a table: It contains a record for each telephone subscriber, and each subscriber's details are contained in three fields - name, address and telephone.
4.What is meant by a record?
a)Collection of related fields. or A record contains all the information about a single 'member' of a table. In a students table, each student's details (name, date of birth, contact details, and so on) will be contained in its own record. Records are also known as tuples in technical relational database.
5)What is meant by field?
a) a Fields describe a single aspect of each member of a table. A student record, for instance, might contain a last name field, a first name field, a date of birth field and so on.
6)what is data?
a)Collection of interrelated data or tables is as database.
2.what is the use of Database?
a) It is used to store the data in the table form.
3.what is meant by a table?
a)collection of records or a table is a set of data elements (values) that is organized using a model of vertical columns(which are identified by their name) and horizontal rows. A table has a specified number of columns, but can have any number of rows. Each row is identified by the values appearing in a particular column subset which has been identified as a candidate key.
(or)
A single store of related information. A table consists of records, and each record is made up of a number of fields. Just to totally confuse things, tables are sometimes called relations. You can think of the phone book as a table: It contains a record for each telephone subscriber, and each subscriber's details are contained in three fields - name, address and telephone.
4.What is meant by a record?
a)Collection of related fields. or A record contains all the information about a single 'member' of a table. In a students table, each student's details (name, date of birth, contact details, and so on) will be contained in its own record. Records are also known as tuples in technical relational database.
5)What is meant by field?
a) a Fields describe a single aspect of each member of a table. A student record, for instance, might contain a last name field, a first name field, a date of birth field and so on.
6)what is data?
a)collection of raw facts.
What Can SQL do?
- SQL can execute queries against a database
- SQL can retrieve data from a database
- SQL can insert records in a database
- SQL can update records in a database
- SQL can delete records from a database
- SQL can create new databases
- SQL can create new tables in a database
- SQL can create stored procedures in a database
- SQL can create views in a database
- SQL can set permissions on tables, procedures, and views.
What is SQL? , What Can SQL do?
- SQL stands for "Structure Query Language" , used to Communicate with the Database. In order to create,retrieve,update Database.
- SQL is a standard language for accessing and manipulating databases.
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