Delete using left outer join in Postgres

Question

I am switching a database from MySQL to Postgres SQL. A select query that worked in MySQL works in Postgres but a similar delete query does not.

I have two tables of data which list where certain back-up files are located. Existing data (ed) and new data (nd). This syntax will pick out existing data which might state where a file is located in the existing data table, matching it against equal filename and path, but no information as to where it is located in the new data:

SELECT ed.id, ed.file_name, ed.cd_name, ed.path, nd.cd_name FROM tv_episodes AS ed LEFT OUTER JOIN data AS nd ON ed.file_name = nd.file_name AND  ed.path = nd.path WHERE ed.cd_name = 'MediaLibraryDrive' AND nd.cd_name IS NULL; 

I wish to run a delete query using this syntax:

DELETE ed FROM tv_episodes AS ed LEFT OUTER JOIN data AS nd ON ed.file_name = nd.file_name AND  ed.path = nd.path WHERE ed.cd_name = 'MediaLibraryDrive' AND nd.cd_name IS NULL; 

I have tried DELETE ed and DELETE ed.* both of which render syntax error at or near "ed". Similar errors if I try without the alias of ed. If I attempt

DELETE FROM tv_episodes AS ed LEFT  JOIN data AS nd..... 

Postgres sends back syntax error at or near "LEFT".

I'm stumped and can't find much on delete queries using joins specific to psql.

Answer 1

As others have noted, you can't LEFT JOIN directly in a DELETE statement. You can, however, self join on a primary key to the target table with a USING statement, then left join against that self-joined table.

DELETE FROM tv_episodes USING tv_episodes AS ed LEFT OUTER JOIN data AS nd ON    ed.file_name = nd.file_name AND     ed.path = nd.path WHERE    tv_episodes.id = ed.id AND    ed.cd_name = 'MediaLibraryDrive' AND nd.cd_name IS NULL; 

Note the self join on tv_episodes.id in the WHERE clause. This avoids the sub-query route provided above.