Qt's open source license (GPL or LGPL)

Question

Ive been reading about Qt and its licensing and ive come across this part:

Qt is available under different licensing options designed to accommodate the needs of our various users:

Qt licensed under commercial licenses is appropriate for development of proprietary/commercial software where you do not want to share any source code with third parties or otherwise cannot comply with the terms of the GNU LGPL version 3. Qt licensed under the GNU Lesser General Public License (LGPL) version 3 is appropriate for the development of Qt applications provided you can comply with the terms and conditions of the GNU LGPL version 3 (or GNU GPL version 3).

Im confused, because some modules of Qt (QtCharts and QSql for example) state that the module is:

available under free software licenses. Since Qt 5.4, these free software licenses are GNU Lesser General Public License, version 3, or the GNU General Public License, version 2

i still dont understand which license do i have to comply with, is it GPL or LGPL ? do i get to choose which is better for my project ?

Note: Im only talking about Qt Community, the commercial license is out of my reach for now.

Thank you

Answer 1

Most Qt modules are licensed under the LGPL, but some are available under only the GPL. The Qt Modules page lists the (currently) six modules in Qt 5 that are not available under the LGPL. Qt Charts is one such module not available under the LGPL. One the other hand, Qt SQL is available under the LGPL.

Your confusion over the "LGPL or GPL" language is understandable, and it is an ambiguity inherent in the English language. When we make the broad statement about Qt, "All Qt modules are available under the LGPL or GPL," we specifically mean, "For every module, it is the case that either the LGPL or the GPL applies to that module, but possibly not both -- some modules are not available under the LGPL." Conversely, the statement "The Qt SQL module is available under the LGPL or GPL," means that you may select either license.

This information is available in legally-rigorous language within the Qt project artifacts themselves. For example, one of the Qt SQL .h header file says:

** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software [...]
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 [...]
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or (at your option) the GNU General
** Public license version 3 [...]

This clearly indicates that the "or" mentioned in the documentation means that you may choose either license for Qt SQL.