Foreign key relationship among tables in SQL

[Satchel]

Hello friends I am an IT student , I am looking forward to be a DBA , but for that I know that I will have to do a lot of hard work and do my query language . So for that reason I want to post and ask something about the tables and their relationship , I was eager to know about the foreign key relation ship being established among the tables and entities. ?

[Dwarner]

I am not quite sure about it , but I can tell you that you can do this with the help of a primary key. Since you know that there is a unique and not null key called as private key in any table , so if that same column is used as some column on another table the n there is a parent and child relationship being established and thus that column becomes the foreign key of the table.

[Jacques25]

A relationship between 2 entities is set up when the data in one of the columns in the primary table go with the data in a column in the next table. To understand this further you will have to comprehend SQL relational notions– Primary Key and Foreign Key. Primary Key is a field or a grouping of columns that exclusively recognizes each row in a table. Thus a relationship is established.

[Villiers]

Foreign Key is a field or a grouping of columns whose values go with a Primary Key in a particular table. In the the majority of ordinary situations the relationship between 2 entities go with the Primary Key in one of the entities with a Foreign Key in the following table. But always remember that a primary key is always having unique and not null values. It cannot have duplicate values.

[Ronchi]

There are 3 kinds of relations between entities – One-To-Many relationship , and then there is Many-To-Many and in there is last that shows One-To-One. The relation that was formed in the one of the relations in One-To-Many kind of relation and is the most ordinary of the 3 kind. In One-To-Many relation a tuple in one of the tables can have a lot of matching tuples in the subsequent table, but a row the second table can match only one row in the first table.