#codEasy

THREE LEVELS OF DATA INDEPENDENCE It divides the entire system into three inter-related but independent modules: Physical Level: Here, information about the location of database objects in the data store is kept. Various DBMS users are unaware of the locations of these objects. The Physical level of database describes how the data is stored in secondary storage devices such as disks and tapes. Conceptual Level: Here, data is represented in the form of various tables. For Example, STUDENT database may contain NAME and COURSE tables, but the users are unaware of their storage. It refers to what kind of data to be stored in a database. External Level: Here, it specifies the view of data in terms of conceptual level tables. It can generate different views of the database for different users. It focuses main on data abstraction.  Data Independence: It means change of data at one level must not affect the another level. Physical Data Independence: Any change in the physical location of t...

  SQL A  Database  is a collection of data which is organized for easy access and efficient management and updating. It is made of  tables  that store the relevant information. Database Tables A  table  stores data in an organized way consisting of rows and columns similar to the one which we see in Microsoft Excel. Database often contains multiple tables each created and designed for a specific purpose. For example we create a table of Patient Names and their contact details in a particular hospital.  Each  table  has own set of fields based on the data it can store.  A Table can have specified number of columns but can have any number of rows. Primary Key A Primary key is a field in the table that uniquely defines the table records. It must contain a unique value for each row and must not contain  NULL  values.  For Example , The column which contains the value ID would be a good choice for a primary key in the tabl...