Basic Database Features
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
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.
A query is
a type of command that retrieves data from the server.
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.
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 :