Different Type of keys in Database Managemenet System.



All super, candidate and primary, secondary keys are used to uniquely distinguish all rows in data base. But the main difference between them is.


  • Super 🔑-superset of candidate keys
  • Candidate 🔑-subset of super key, it is a single key or least combination of feild that uniquely  identifies every tuple.
  • Primary 🔑- it is a candidate key that is most appropriate to become main key for the table.
  • Secondary 🔑-candidate keys which are not selected as primary keys.



  • Non-key attributes (attributes other than candidate keys)
  • Non prime attributes (attributes other than primary key)




Foreign 🔑??


  • It is a feild in one table that uniquely identifies a row in another table
  • They are constraints between column of tables.

Example:





Comments

Post a Comment

Popular posts from this blog

FC Barcelona vs Real Madrid -El Clasico Rivalry.

Image
                              El Clasico The Story of the Rivalry between FC Barcelona and Real Madrid  The rivalry comes about as  Madrid  and  Barcelona  are the two largest cities in Spain, and they are sometimes  identified  with opposing political positions, with Real Madrid viewed as representing  Spanish nationalism  and Barcelona viewed as representing  Catalan nationalism . It is considered one of the biggest club  football  games in the world, and is among the most viewed annual sporting events.  It has always been a heated match, from both sides. Political background: The rivalry between the the two most successful clubs in football started with an oft-ignored political backstory and contrasts in how both clubs were made.  FC Barcelona was founded by --> Joan Gamper along with several foreign-born players in 1899. Real Madrid  was founded by  -->Spaniards at the helm in 1902.  Madrid had been long considered as the political and soc
Read more

1NF,2NF, 3NF Normalization

Image
If you want to know more about normalization and keys refer this posts: http://vinayjallipalli75996.blogspot.in/2016/12/different-type-of-keys-in-database.html http://vinayjallipalli75996.blogspot.in/2016/12/normalization-in-database.html 1NF : Composite attribute are not allowed. 2NF: All non prime attributes are fully functional dependent with primary key.that is non prime attributes should not be partially dependent on primary key. 3NF: There should not be any dependency between non prime attributes.               Example For 3NF (see the below fig.): student id,name, dob , street,city, zip,state->>>                        1)sid,name,dob                        2)zip, city, state, Street becoz zip is dependent on rest of the three.
Read more

Memory Management (Contiguous and Non-Contiguous ).

Image
                MEMORY MANAGEMENT Background: Memory consists of a large array of words or bytes, each with its own address. The CPU fetches instructions from memory according to the value of the program counter. These instructions may cause additional loading from and storing to specific memory addresses. Just as processes share the CPU, they also share physical memory Memory management is subdividing memory to accommodate multiple processes.  Memory needs to be allocated to ensure a reasonable supply of ready processes to consume available processor time. Memory Allocation: There are two types of memory allocation techniques: Contiguous. Non - Contigous. 1.Contiguous Memory Allocation: Fixed size partitioning . Dynamic Partitioning . Fixed size partitioning -  (Causes internal fragmentation) : Each partition contain exactly one process. Degree of multiprogramming bound by # of partitions –A program may not fit in a partition. The p
Read more