Bug 1752688: Need to check what flavour of mysql is being used

Because MariaDB does not have JSON cast type but does have a higher
version number than 5.7

behatnotneeded

Change-Id: I5a66ddb8c382a68fde189b420088bb29ef06893c
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>

htdocs/lib/db/upgrade.php

@@ -5171,7 +5171,7 @@ function xmldb_core_upgrade($oldversion=0) {
 
         log_debug('Adjust existing "event_log" data to fit new table structure');
         $db_version = get_db_version();
-        if (is_mysql() && version_compare($db_version, '5.7.8', '>=')) {
+        if (is_mysql() && mysql_get_type() == 'mysql' && version_compare($db_version, '5.7.8', '>=')) {
             // Update the event_log table using the json datatype
             // by converting the data field to json.
             // This datatype was introduced in Mysql 5.7.8.

htdocs/lib/dml.php

@@ -1562,6 +1562,22 @@ function is_mysql() {
     return (strpos(get_config('dbtype'), 'mysql') === 0);
 }
 
+function mysql_get_type() {
+    if (!is_mysql()) {
+        throw new SQLException('mysql_get_type() expects a mysql database');
+    }
+    $mysqltype = mysql_get_variable('version_comment');
+    if (stripos($mysqltype, 'MariaDB') !== false) {
+        return 'mariadb';
+    }
+    else if (stripos($mysqltype, 'Percona') !== false) {
+        return 'percona';
+    }
+    else {
+        return 'mysql';
+    }
+}
+
 /**
  * function to convert an array to
  * an array of placeholders (?)