How Can I Use LEFT JOINs to Retrieve Person and Fear Data from Three MySQL Tables?

MySQL LEFT JOIN Three Tables for Fearful Persons

To retrieve a list of individuals with their associated fears, you must seamlessly merge three interconnected tables:

• Persons: Includes essential information about individuals, such as their PersonID, Name, and SS (Social Security number).
• Fears: Lists various fears, each assigned a unique FearID.
• Person_Fear: Serves as the bridge between individuals and fears, with ID, PersonID, and FearID.

Modifying Your LEFT JOIN Query

Your initial attempt at creating a LEFT JOIN encountered an issue. The specified join condition, person_fear.personid = person_fear.fearid, doesn't align with the desired relationship between the tables. To correctly link the Persons table to the Fears table through the Person_Fear intermediary, use this modified code:

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

Explanation of the Modified Query

• LEFT JOIN merges the Persons table with the Person_Fear table, where each individual's PersonID is matched to the corresponding PersonID in Person_Fear. This ensures that every person is included in the results, even if they have no associated fears.
• An INNER JOIN links the Person_Fear table to the Fears table based on the FearID column. This operation retrieves only those fears that are explicitly connected to individuals via the Person_Fear table.
• The ON clauses ensure that the PersonID in the Persons table corresponds to the PersonID in the Person_Fear table, which in turn matches the FearID in the Fears table.

Alternative Query Syntax

An alternative way to write the LEFT JOIN query is:

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 syntax is equally effective in retrieving the desired data, utilizing two LEFT JOINs to connect the tables.

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