diff --git a/lib/dml/oci_native_moodle_database.php b/lib/dml/oci_native_moodle_database.php
index b5d60188891..6db6a7bca86 100644
--- a/lib/dml/oci_native_moodle_database.php
+++ b/lib/dml/oci_native_moodle_database.php
@@ -438,9 +438,10 @@ class oci_native_moodle_database extends moodle_database {
         $indexes = array();
         $tablename = strtoupper($this->prefix.$table);
 
-        $sql = "SELECT i.INDEX_NAME, i.UNIQUENESS, c.COLUMN_POSITION, c.COLUMN_NAME, ac.CONSTRAINT_TYPE
+        $sql = "SELECT i.INDEX_NAME, i.INDEX_TYPE, i.UNIQUENESS, c.COLUMN_POSITION, c.COLUMN_NAME, e.COLUMN_EXPRESSION, ac.CONSTRAINT_TYPE
                   FROM ALL_INDEXES i
                   JOIN ALL_IND_COLUMNS c ON c.INDEX_NAME=i.INDEX_NAME
+             LEFT JOIN ALL_IND_EXPRESSIONS e ON (e.INDEX_NAME = c.INDEX_NAME AND e.COLUMN_POSITION = c.COLUMN_POSITION)
              LEFT JOIN ALL_CONSTRAINTS ac ON (ac.TABLE_NAME=i.TABLE_NAME AND ac.CONSTRAINT_NAME=i.INDEX_NAME AND ac.CONSTRAINT_TYPE='P')
                  WHERE i.TABLE_NAME = '$tablename'
               ORDER BY i.INDEX_NAME, c.COLUMN_POSITION";
@@ -463,6 +464,20 @@ class oci_native_moodle_database extends moodle_database {
                                              'unique'  => ($record['UNIQUENESS'] === 'UNIQUE'),
                                              'columns' => array());
             }
+
+            // If this is an unique, function-based, index, then we have to look to the expression
+            // and calculate the column name by parsing it.
+            if ($record['UNIQUENESS'] === 'UNIQUE' && $record['INDEX_TYPE'] === 'FUNCTION-BASED NORMAL') {
+                // Only if there is an expression to look.
+                if (!empty($record['COLUMN_EXPRESSION'])) {
+                    // Let's parse the usual code used for these unique indexes.
+                    $regex = '/^CASE *WHEN .* THEN "(?<column_name>[^"]+)" ELSE NULL END *$/';
+                    if (preg_match($regex, $record['COLUMN_EXPRESSION'], $matches)) {
+                        $record['COLUMN_NAME'] = $matches['column_name'] ?? $record['COLUMN_NAME'];
+                    }
+                }
+            }
+
             $indexes[$indexname]['columns'][] = strtolower($record['COLUMN_NAME']);
         }
 
diff --git a/lib/dml/tests/dml_test.php b/lib/dml/tests/dml_test.php
index 7337b3e050b..23f9b7a3bfa 100644
--- a/lib/dml/tests/dml_test.php
+++ b/lib/dml/tests/dml_test.php
@@ -719,6 +719,41 @@ EOD;
         $this->assertSame('id', $composed['columns'][1]);
     }
 
+    /**
+     * Let's verify get_indexes() when we mix null and not null columns in unique indexes.
+     *
+     * Some databases, for unique indexes of this type, need to create function indexes to
+     * provide cross-db behaviour. Here we check that those indexes don't break get_indexes().
+     *
+     * Note that, strictly speaking, unique indexes on null columns are far from ideal. Both
+     * conceptually and also in practice, because they cause DBs to use full scans in a
+     * number of situations. But if we support them, we need to ensure get_indexes() work on them.
+     */
+    public function test_get_indexes_unique_mixed_nullability() {
+        $DB = $this->tdb;
+        $dbman = $this->tdb->get_manager();
+        $table = $this->get_test_table();
+        $tablename = $table->getName();
+
+        $table->add_field('id', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, XMLDB_SEQUENCE, null);
+        $table->add_field('nullable01', XMLDB_TYPE_INTEGER, 10, null, null, null, null);
+        $table->add_field('nullable02', XMLDB_TYPE_INTEGER, 10, null, null, null, null);
+        $table->add_field('nonullable01', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0');
+        $table->add_field('nonullable02', XMLDB_TYPE_INTEGER, '10', null, XMLDB_NOTNULL, null, '0');
+        $table->add_key('primary', XMLDB_KEY_PRIMARY, array('id'));
+        $indexcolumns = ['nullable01', 'nonullable01', 'nullable02', 'nonullable02'];
+        $table->add_index('course-id', XMLDB_INDEX_UNIQUE, $indexcolumns);
+        $dbman->create_table($table);
+
+        $indexes = $DB->get_indexes($tablename);
+        $this->assertIsArray($indexes);
+        $this->assertCount(1, $indexes);
+
+        $index = array_shift($indexes);
+        $this->assertTrue($index['unique']);
+        $this->assertSame($indexcolumns, $index['columns']);
+    }
+
     public function test_get_columns() {
         $DB = $this->tdb;
         $dbman = $this->tdb->get_manager();