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Constraints

NOT NULL CONSTRAINT -    Ensures that a column cannot have a null value. DEFAULT CONSTRAINT -    Provides a default value for a column when none is specified  UNIQUE CONSTRAINT -   Ensures that all values in columns are different  CHECK CONSTRAINT -   Makes sure that all values in a column satisfy certain criteria  PRIMARY KEY CONSTRAINT -   Used to uniquely identify a row in the table  FOREIGN KEY CONSTRAINT -   Used to ensure referential integrity of the data  Primary Key - is used uniquely to identify each row in a table . It can consist of one or more columns on a table . When Multiple columns are used on a table it is called composite key.  Foreign Key - Foreign key is a column or columns that references a column most often primary key of another table . The purpose of foreign key is to maintain referential integrity of the data. Pg admin  Data base - training - right click on training - query click  Always add semi colen to run the query  Int - integer  varchar - variable charact
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Colour Contrast

 Colour Contrasting means the difference in light between Foreground and Background.

Example - When you have a very vibrant background and in the foreground you have the same level of vibrant colour it makes awful to see and therefore we can fix them by adjusting the foreground colour through tones , tints and saturation of the colours . 

Contrast Ratio - It is the value assigned to the difference in light between foreground and background . 

It is said that high Contrast Ratio , the easier it gets to read the content on the screen. 

  • Never use Pure Black on Pure White and vice vera . It causes Digital Eye Strain and hurts users eye. Instead you can use a very dark grey or a very light grey and vice vera.

  • Don't use a bright colour on a bright colour , It cannot let your elements stand out . You can use bright colour on a dark shade. 

  • Always check your colours on both light and dark backgrounds . You can adjust the colour of the background to look good. 

  • Always validate your colours by checking the contrast Ratio .

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