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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 Formulae

 Monochromatic - It uses only one colour or Hue . It is used by choosing one colour from the colour wheel and using that create variations from that particular colour through saturation (intensity) and value (brightness). Monochromatic guarantees to work together well. 


Complementary - It takes 2 opposite directions colours from the colour wheel . Such as Blue and Orange or Yellow and Purple , Its great when you want to use high contrasting colour into your design. 


Split - Complementary - It takes Colours on either side of the compliment . It helps in playing with 3 different colours while keeping the same level of contrast. 


Analogous - They Take colours that are next to each other such as yellow , greens or Blues and purple. 


Triadic - They use 3 colours that are evenly spaced . They form a triangle in the colour wheel . These are usually a vibrant colours and therefore should be used wisely.


Tetradic - This colour scheme takes 2 sets of complementary colours and forms a rectangle in the colour wheel. It works great when one colour is considered main and other compliments that one main colour. 

One make make different tints , shades and tones from the colour .

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