From c9da36d73194ab1da0e807a6977da054fa6261ba Mon Sep 17 00:00:00 2001
From: Cameron Ball <cameronball@catalyst-au.net>
Date: Wed, 10 Aug 2022 15:09:20 +0800
Subject: [PATCH] MDL-74910 core_files: Return SQL to initial state

MDL-73727 aimed to improve the performance of the
get_conversions_for_file SQL. Unfortunately it also
changed the behvaiour of the SQL.

On further investigation, there is nothing wrong with
the SQL. This patch returns it back to its initial state.
---
 files/classes/conversion.php | 37 +++++++-----------------------------
 1 file changed, 7 insertions(+), 30 deletions(-)

diff --git a/files/classes/conversion.php b/files/classes/conversion.php
index 0a2e8610ed56d..f0a181900477f 100644
--- a/files/classes/conversion.php
+++ b/files/classes/conversion.php
@@ -128,36 +128,13 @@ public static function get_conversions_for_file(stored_file $file, $format) {
 
         // Fetch actual conversions which relate to the specified source file, and have a matching conversion record,
         // and either have a valid destination file which still exists, or do not have a destination file at all.
-        $dbfamily = $DB->get_dbfamily();
-        switch ($dbfamily) {
-            // For certain DB engines, use a more optimised query.
-            case 'mysql':
-            case 'postgres':
-                $sql = "SELECT {$sqlfields}
-                          FROM {" . self::TABLE . "} c
-                          JOIN (SELECT id
-                                  FROM {files}
-                                 WHERE contenthash = :ccontenthash
-                                 LIMIT 1
-                               ) conversionsourcefile ON conversionsourcefile.id = c.sourcefileid
-                     LEFT JOIN {files} conversiondestfile ON conversiondestfile.id = c.destfileid
-                         WHERE c.targetformat = :cformat
-                           AND (c.destfileid IS NULL
-                                OR conversiondestfile.id IS NOT NULL)";
-                break;
-
-            // For everything else, use the standard cross-db compatible query.
-            default:
-                $sql = "SELECT {$sqlfields}
-                          FROM {" . self::TABLE . "} c
-                    INNER JOIN {files} conversionsourcefile ON conversionsourcefile.id = c.sourcefileid
-                     LEFT JOIN {files} conversiondestfile ON conversiondestfile.id = c.destfileid
-                         WHERE conversionsourcefile.contenthash = :ccontenthash
-                           AND c.targetformat = :cformat
-                           AND (c.destfileid IS NULL
-                                OR conversiondestfile.id IS NOT NULL)";
-                break;
-        }
+        $sql = "SELECT {$sqlfields}
+                  FROM {" . self::TABLE . "} c
+                  JOIN {files} conversionsourcefile ON conversionsourcefile.id = c.sourcefileid
+             LEFT JOIN {files} conversiondestfile ON conversiondestfile.id = c.destfileid
+                 WHERE conversionsourcefile.contenthash = :ccontenthash
+                       AND c.targetformat = :cformat
+                       AND (c.destfileid IS NULL OR conversiondestfile.id IS NOT NULL)";
 
         // Fetch a empty conversion record for each source/destination combination that we find to match where the
         // destination file is in the correct filearea/filepath/filename combination to meet the requirements.