Relational Data Model: Relational data model was proposed by Dr. E.F. Codd, a researcher in IBM. This was the first time a real database was used and data was stored in rows and columns. It all started in 1970 by his article titled “A Relational Model of Data for Large Shared Data Banks”.
Concept of Table: In realtional data model, concept of table was introduced.
1) A table is a collection of rows and columns.
2) Every table in a database has a unique name.
3) Also, each column has a unique name.
4) Columns are placed in a left to right order.
5) A table must have atleast one column.
6) A table has a mximum of 255 columns.
7) Rows can be in any order.
8) A table can have any number of rows.
9) A table with can have no rows whatsoever.
10) A table with 0 rows is called as an empty table.
Primary key: In a relational model every row is unique. From this concept only, the name relational is evolved. A primary key is a unique value set to identify a row in a table. A primary key is actually a column or a collection of columns whose values ca be used to uniquely identify each row in a table.
Foreign key: A foregin key is a column in a table whose value matches primary key in another table. Primary and foerign keys are used to create parent and child relationships in the tables.