Where is information on programming techniques for SQL?

In a sense, the 4GL is an example of 'black box' processing, each generation (in the sense of the page) is further from the machine (see the Computer Science history in regard to data structure improvements and information hiding). It's this latter nature that is directly associated with 4GL having errors that are harder, in many cases, to debug. In terms of applications, a 4GL could be business oriented or it could deal with some technical domain. Being further from the machine implies being closer to domain. Given the wide disparity of concepts and methods across domains, 4GL limitations lead to recognition of the need for the 5GL.