PostgreSQL Example – How to Create Left Join Tables

Left Join Tables

Create Table Of Adventurers

- Create table called adventurers
CREATE TABLE adventurers (
    - string variable
    name varchar(255),
    - integer variable
    age int,
    - string variable
    race varchar(255)

Create Table Of Adventurer’s Equipment

- Create table called equipment
CREATE TABLE equipment (
    - string variable
    name varchar(255),
    - string variable
    clothes varchar(255),
    - string variable
    weapon varchar(255)

Insert Rows Into Adventurers Table

INSERT INTO adventurers (name, age, race)
VALUES ('Dallar Woodfoot', 25, 'Elf'),
       ('Cordin Garner', 29, 'Elf'),
       ('Keat Knigh', 24, 'Dwarf'),
       ('Colbat Nalor', 124, 'Dwarf')

Insert Rows Into Equipment Table

INSERT INTO equipment (name, clothes, weapon)
VALUES ('Dallar Woodfoot', 'Leather Armor', 'Axe'),
       ('Keat Knigh', 'Robe', 'Bow'),
       ('Tasar Keynelis', 'Tunic', 'Axe'),
       ('Sataleeti Iarroris','Chainmail', 'Axe')

Left Join Tables

- Return the name of people from the adventurers table, age, race, clothes, and weapon
SELECT, age, race, clothes, weapon FROM adventurers
- Left join with the equipment table
    - Using the name as the merge key contained in both tables
    ON ( =
name age race clothes weapon
Dallar Woodfoot 25 Elf Leather Armor Axe
Cordin Garner 29 Elf NULL NULL
Keat Knigh 24 Dwarf Robe Bow
Colbat Nalor 124 Dwarf NULL NULL


Python Example for Beginners

Two Machine Learning Fields

There are two sides to machine learning:

  • Practical Machine Learning:This is about querying databases, cleaning data, writing scripts to transform data and gluing algorithm and libraries together and writing custom code to squeeze reliable answers from data to satisfy difficult and ill defined questions. It’s the mess of reality.
  • Theoretical Machine Learning: This is about math and abstraction and idealized scenarios and limits and beauty and informing what is possible. It is a whole lot neater and cleaner and removed from the mess of reality.

Data Science Resources: Data Science Recipes and Applied Machine Learning Recipes

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