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Ch. 9 Data Integration (Join (Types of Joins (Inner Join :star: (Creates a…

- - - - Creates a table within in the two tables. NO Null values, only values found in both tables are shown in Inner Join
      - Overall: gives us the most accurate//complete information,
        complete info meaning- occurrences that happened on both tables
    - - Left/Right Join :star:
        
        Left Join: Left table is the primary table. Which means the Left table values can not be null. The Right table values only fill the Left table values and fill Null IF Left table values not found on Right table
        
        ex: 2 Tables - Cust and Invoice
        Cust has - ID 1 and 2
        Invoice has - Cust 1 and 3
        Left Join will show:
        ID 1 and 2 and Invoice 1 but Invoice for
        ID 2 will be Null
        
        Overall: Gives us max info the for Base table (Cust above), max info meaning- all occurrences possible of base table keys
      - Fill Outer Join
        
        Joins with Nulls and Fully Joins two tables on common Key
- - - - Multiple DBs: this entails, different ID keys or composite keys
      - Common Ex of Union Use Case: Integration of Training and Test Cases
        
        ML Comp: 2 pieces - Training and Test Cases
        
        Test: someone evaluates your your Training Model
        
        Training - Trains to ML Model