How Can I Efficiently LEFT JOIN Three Tables to Retrieve Person-Fear Relationships in MySQL?

MySQL LEFT JOIN 3 Tables for Fear and Person Relationships

In a set of three relational tables, one can retrieve a comprehensive list of persons along with any associated fears. This can be achieved through a LEFT JOIN query involving the 'Persons,' 'Fears,' and 'Person_Fear' tables.

The 'Persons' table holds personal information, including 'Name' and 'SS' (social security number), while the 'Fears' table lists potential fears, and the 'Person_Fear' table establishes the relationship between people and their fears.

In a previous attempt, a LEFT JOIN query was constructed but encountered errors. The incorrect code provided was:

SELECT persons.name, 
       persons.ss, 
       fears.fear 
FROM   persons 
       LEFT JOIN fears 
              ON person_fear.personid = person_fear.fearid 

The error stems from incorrectly referencing 'person_fear' twice in the join clause. Instead, the join should connect 'Persons' to 'Person_Fear' based on their 'PersonID' column and 'Person_Fear' to 'Fears' using 'FearID.'

Here's a corrected LEFT JOIN query:

SELECT Persons.Name, Persons.SS, Fears.Fear 
FROM Persons
LEFT JOIN Person_Fear ON Person_Fear.PersonID = Persons.PersonID
LEFT JOIN Fears ON Person_Fear.FearID = Fears.FearID

This LEFT JOIN query constructs a list that contains all persons, including those without any associated fears. The result set will include the 'Name,' 'SS,' and 'Fear' columns for each record.

Alternatively, the following LEFT JOIN query achieves the same result:

SELECT Persons.Name, Persons.SS, Fears.Fear 
FROM Persons
LEFT JOIN Person_Fear
    INNER JOIN Fears ON Person_Fear.FearID = Fears.FearID
ON Person_Fear.PersonID = Persons.PersonID

By utilizing LEFT JOINs effectively, database queries can retrieve comprehensive and interconnected data from multiple tables.

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