What is the method for obtaining all records from a third table while filtering through the join of a different table, even if no matches exist?

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The method is to use a LEFT JOIN clause to join the two tables and then include the third table in the query with another LEFT JOIN clause. This will ensure that all records from the third table are returned, even if no matches are found in the join between the first two tables.

The query would look something like this:

SELECT * FROM table1 LEFT JOIN table2 ON table1.id = table2.table1id LEFT JOIN table3 ON table2.id = table3.table2id

In this example, we are joining table1 and table2 on their respective id columns. We then use another LEFT JOIN clause to include table3 in the query, joining it with table2 on its id column. This will return all records from table3, regardless of whether any matches were found in the join between table1 and table2.

Note that if you only want to return records from table3 that have matches in the join between table1 and table2, you can use an INNER JOIN clause instead of a LEFT JOIN clause for the join between table2 and table3.