MySQL: remove the version number checks in favor of actual functionality

MariaDB library version 3.2 no longer returns the server version in the
10.x range but the library version itself, which is lower than 4.x. That
meant we concluded the server did not support prepared statements.

And because of the lack of prepared statements, all QDateTime
conversions failed, because of the timezone. I don't know if this was
intended or what, but it's a side issue.

[ChangeLog][QtSql][MySQL] Fixed the detection of whether the client and
server support prepared statements. This was caused by the mariadb
connector library reporting its own version numbers (starting in version
3.2) instead of the server version.

Fixes: QTBUG-95071
Pick-to: 5.15 6.2
Change-Id: I4a40ccbd3321467a8429fffd1699bc089ba706e6
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
Reviewed-by: Fabian Vogt <fabian@ritter-vogt.de>

1 files changed, 15 insertions, 2 deletions

diff --git a/src/plugins/sqldrivers/mysql/qsql_mysql.cpp b/src/plugins/sqldrivers/mysql/qsql_mysql.cpp
index 12e15bfc47..5358d6a94e 100644
--- a/src/plugins/sqldrivers/mysql/qsql_mysql.cpp
+++ b/src/plugins/sqldrivers/mysql/qsql_mysql.cpp
@@ -121,6 +121,20 @@ static inline QVariant qDateTimeFromString(QString &val)
 #endif
 }
 
+// check if this client and server version of MySQL/MariaDB support prepared statements
+static inline bool checkPreparedQueries(MYSQL *mysql)
+{
+    std::unique_ptr<MYSQL_STMT, decltype(&mysql_stmt_close)> stmt(mysql_stmt_init(mysql), &mysql_stmt_close);
+    if (!stmt)
+        return false;
+
+    static const char dummyQuery[] = "SELECT ? + ?";
+    if (mysql_stmt_prepare(stmt.get(), dummyQuery, sizeof(dummyQuery) - 1))
+        return false;
+
+    return mysql_stmt_param_count(stmt.get()) == 2;
+}
+
 class QMYSQLResultPrivate;
 
 class QMYSQLResult : public QSqlResult
@@ -1276,8 +1290,7 @@ bool QMYSQLDriver::open(const QString& db,
             qWarning() << "MySQL: Unable to set the client character set to utf8.";
     }
 
-    d->preparedQuerysEnabled = mysql_get_client_version() >= 40108
-                        && mysql_get_server_version(d->mysql) >= 40100;
+    d->preparedQuerysEnabled = checkPreparedQueries(d->mysql);
 
 #if QT_CONFIG(thread)
     mysql_thread_init();