Question

A previous employee at my office constructed a php script that uses curly braces in the a SQL query. I understand that it would normally work for things like encapsulating array variables, but this query doesn’t have any PHP variables in the string. Can someone clarify what the table being generated in the FROM section of the query is actually requiring the curly braces for, and what the OJ stands for?

SELECT
  DISTINCT ra.folder_id,
  pd.id,
  f.name,
  pd.descriptor_text
FROM
  { 
    OJ permission_descriptors pd
    LEFT JOIN permission_descriptor_users pdu
    ON pdu.descriptor_id = pd.id
  }
  role_allocations ra,
  folders f
WHERE
  pdu.descriptor_id IS NULL AND
  pd.id = ra.permission_descriptor_id AND
  pd.id != 1
  ra.folder_id = f.id
ORDER BY
  ra.folder_id

Answer 1

MySQL supports this alternative syntax for an Outer Join.
However that does not mean that it should be used.

1. It can be problematic to have RDBMS-specific code if at some point you need switch to another RDBMS.
2. Googling around, it appears that MySQL doesn’t support this syntax for more than 2 joins.

Aside:
Another non-ANSI-compliant issue with the code is the subsequent joins.

This is a quick stab at an ANSI-compliant version (not tested):

SELECT
  DISTINCT ra.folder_id,
  pd.id,
  f.name,
  pd.descriptor_text
FROM
  permission_descriptors pd
  LEFT JOIN permission_descriptor_users pdu
  ON pdu.descriptor_id = pd.id
  LEFT JOIN role_allocations ra
  ON pd.id = ra.permission_descriptor_id 
  LEFT JOIN folders f 
  ON ra.folder_id = f.id

WHERE
  pdu.descriptor_id IS NULL AND
  pd.id <> 1 
ORDER BY
  ra.folder_id;

Other notes:
For inequality != will work, but <> is preferred.