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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 Knowledge

Primary colours - Dominantly used by UI / UX Design. We must use the brands colour as the primary colour . 

Secondary Colours- The optional set of colours to make the design more interesting if they are really needed. Its basically for the design to pop. 

Accent Colours - Are used to emphasise or highlight some information such as texts , sliders , links and progress bar. Once you pick the primary colour , you may pick the harmony colours like monochromatic , complimentary etc to make accent colours . 

Semantic Colours - They are used for warning , error , success and information . You should use Yellow for warning , Red for error , Green for Success and Blue for information. They are suggested by colour psychology. 

Neutral Colours - These colours are mostly used for backgrounds . they let all other colours to pop up from the design. 

Chart and Data Visualisation Colours - Just like secondary colours having these colours are optional depending on the type of project . Chart , heat maps or tree maps are primarily coloured . One must create a set of 10 to 20 colours using the following guidelines . 

You can make a Categorical Colour Scheme by suing multiple colour that contrast to each other in a certain order , its good for line charts , bar charts etc . Since these are contrasting , use them when you want to use the data distinctively . 

One Scheme is Sequential Order , Its a gradual transformation of colours form light to dark and vice versa , its suitable for tree map or heat map . 

Last Type of Colour Scheme is Diverging where negative and positive values are there to present . We must not use it for categorical scales.


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