There are many ways to give instructions to a computer: an electrical engineer might write a MATLAB program; a database administrator might write an SQL script; a hardware engineer might write in Verilog; and an accountant might write a spreadsheet with embedded formulas. Aside from the difference in language used in each of these examples, there is an important difference in form and idiom. Each uses a language customized to the job at hand, and each builds computational requests in a form both familiar and productive for programmers (although accountants may not think of themselves as programmers). In short, each of these examples uses a Domain-Specific Language (DSL).
A DSL is a special-purpose language, designed to encapsulate possible computations in a specific domain. In the earlier examples of MATLAB, SQL, Verilog, and spreadsheets, the domains would be scientific modeling, database queries and updates, hardware circuits, and financial computations, respectively. Considering SQL specifically, there is nothing it does that could not be done in Java or C, or any other general-purpose programming language. SQL simply bundles the actions needed to interact with a database into a usable and productive package, and the language becomes the interface to communicate requests to the database engine.
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