SQL

  • Primary key can not be NULL.
  • Normalization is the process of minimizing redundancy and dependency by organizing fields and table of a database.
  • A view is a virtual table which consists of a subset of data contained in a table. Views are not virtually present, and it takes less space to store. View can have data of one or more tables combined, and it is depending on the relationship.  
  • An index is performance tuning method of allowing faster retrieval of records from the table. An index creates an entry for each value and it will be faster to retrieve data. 
  • Database Relationship is defined as the connection between the tables in a database.
  • One to One Relationship.
  • One to Many Relationship.
  • Many to One Relationship.
  • Self-Referencing Relationship.
  • A sub query is a query within another query. 
  •  A DB trigger is a code or programs that automatically execute with response to some event on a table or view in a database. 
  • Datawarehouse is a central repository of data from multiple sources of information.
  • Self-join is set to be query used to compare to itself. This is used to compare values in a column with other values in the same column in the same table.
  • Cross join defines as Cartesian product where number of rows in the first table multiplied by number of rows in the second table. If suppose, WHERE clause is used in cross join then the query will work like an INNER JOIN.
  • TRUNCATE removes all the rows from the table, and it cannot be rolled back. DROP command removes a table from the database and operation cannot be rolled back.  
  • Aggregate functions are used to evaluate mathematical calculation and return single values.

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