Basic Database Features

• Database

  A database is a named collection of schemas, catalogs and  extensions. A client application connects to a PostgreSQL server, with a login username and password  it specifies the name of the database that it wants to access. A client cannot interact with more than one database per connection but it can open any number of connections in order to access multiple databases simultaneously.

  

  

   

• Schema

  A schema is a named collection of objects like tables ,views, indexes, sequences, data types, operators, and functions. Other relational database products use the term catalog.

  

  PostgreSQL Catalog contains system objects which are used to support dbms.

  

• Query

  A query is a type of command that retrieves data from the server.

  

  

• Table (relation, file, class)

  A table is a collection of rows, and rows in turns contain fields or columns. In a SQL query, client must mention the table name , after logging to the database. A FIELD OR COLUMN must be defined with certain data type and hold data of same data type.

• Column (field, attribute)

  A column or filed, is the smallest unit of storage entity in a relational database.  Every column must have a name and data type. The columns are grouped into rows, and rows are grouped into tables. The order of hierarchy is Schema > Table > Columns & Rows

• Tuple : row of values in a relational database