Basic database terminology

                                     Relational schema 

                   an existing idea of how the DB must be organized

Primary key : A column(or set of columns) whose value exists and is unique for every record in a table is called primary key.


Foreign Key :  Identifies the relationship between tables,not the tables themselves.


Unique Key & Null values : Used whenever you would like to specify that you don't want to see duplicate data in a given fields.

Example :

Relationships : Relationships tell you how much of the data from the foreign key field can be seen in the primary key column of the table the data is related to and vice-versa.


One to Many Relation : 


Example : of ONE  toooooo

MANY:


Many to One :





 


Comments

Post a Comment

Popular posts from this blog

preparation analytics

                                                            Preparation Test      date : 28/09/2020    CSS :      1: Explain the CSS “box model” and the layout components that it consists of.             Provide some usage examples.      The CSS box model is a rectangular layout paradigm for HTML elements that consists of the following: Content - The content of the box, where text and images appear Padding - A transparent area surrounding the content (i.e., the amount of space between the border and the content) Border - A border surrounding the padding (if any) and content Margin - A transparent area surrounding the border (i.e., the amount of space between the border and any neighboring elements) Each of t...
Read more

sitemap date format

  Date formating in sitemap.xml file for SEO:     The 'lastmod' element has to be of the format YYYY-MM-DD or YYYY-MM-DDThh:mmTZD so use: gmdate( 'Y-m-d' , strtotime($row[ 'modified' ][ 'value' ])) or gmdate( 'Y-m-d\TH:i:s+00:00' , strtotime($row[ 'modified' ][ 'value' ]))
Read more

SQL INSERT statement

Image
                                                    The INSERT statement - Part I Example :          use employees; SELECT     * FROM     employees LIMIT 10; #insert data insert into employees(     emp_no,     birth_date,     first_name,     last_name,     gender,     hire_date ) values(     999901,     '1999-10-10',     'John',     'wick',     'M',     '2020-08-31'     );     SELECT     * FROM     employees WHERE     emp_no = 999901;                       ...
Read more