How to Properly Left Join with a Filtered Right-Hand Table to Retrieve All Default Settings and Optional Custom Settings?

Left join using filtered left table

This question discusses retrieving data from two tables, where a WHERE clause in the left table prevents the expected results from occurring. The goal is to retrieve all default settings from the settings table and, if available, any role-specific custom settings for a specific role.

Original query:

SELECT `settings`.*, `character_settings`.`value`
FROM (`settings`)
LEFT JOIN `character_settings` 
ON `character_settings`.`setting_id` = `settings`.`id`
WHERE `character_settings`.`character_id` = '1'  

However, this query only returns rows where there is a matching character-specific setting for the specified character (character_id = 1). In order to include default settings (even if no role-specific settings exist), the WHERE clause should be moved to the connection itself:

SELECT  `settings`.*, `character_settings`.`value`
FROM    `settings`
LEFT JOIN 
       `character_settings` 
ON     `character_settings`.`setting_id` = `settings`.`id`
        AND `character_settings`.`character_id` = '1'  

This modified query now effectively performs a left join where the left table (settings) is not filtered by any criteria. Therefore, it retrieves all default settings while optionally including any role-specific settings if they exist.

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