1
Because you have four tables establishing the hierarchy you can simply join all of the elements directly:
SELECT
level1.key1
,level1.key2
,level2.key3
,level3.key4
FROM
table1 level1
LEFT JOIN
table2 level2
ON level2.key2 = level1.key2
LEFT JOIN
table3 level3
ON level3.key3 = level2.key3
1
You are probably using a method to return data which needs unique column names, for example because it uses the column names as keys in a hash. You can add aliases to make the column names unique.
This is the first line of your query with aliases:
SELECT certifications.*, users.name as user_name, company.name as company_name, certstype.name as ...
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