Comparing SQL and Prolog

What they do best

SQL excels at data operations in finite datasets, thanks to its roots in Relational Calculus and Predicate Logic. It is optimized for managing structured, tabular data like customer records or product inventory.

On the other hand, Prolog, being a logic-driven language, shines in areas requiring complex, rule-based reasoning. Also, it has exceptional capabilities in handling inference problems, such as determining genealogical relationships or solving puzzles.

Definition and representation

In Prolog, relations are expressed as facts and rules, while SQL represents relations through tables. An aliased table-expression in SQL can be compared to a rule in Prolog, where both provide a name to associated query logic.

-- SQL
SELECT * FROM employees e WHERE e.department = 'Sales'; -- All hail the salespeople
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-- Prolog
left_of(X, Y) :- location(X, Z), location(Y, W), Z < W. -- No, it's not about politics
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Turing completeness and infinite sets

Prolog flaunts its Turing completeness, allowing it to potentially work with infinite sets, and thus deriving all possible solutions. SQL, however, being a subset of the predicate calculus, doesn't have a Turing complete design and focuses solely on set-based data operations on finite datasets.

Language paradigms and practical applications

SQL's server-language paradigm makes it ideal for handling structured data storage tasks efficiently, think of address lists or inventory tracking. On the contrary, Prolog's client-language paradigm allows it to solve abstract problems, such as language processing, scheduling, or AI modeling, operating less efficiently on everyday storage needs.

Efficiency and expressiveness

SQL is designed to efficiently retrieve structured data by following a specific path. Prolog, using its rule-based logic, can solve complex non-linear problems which SQL might not handle inherently. Despite this, Prolog's deductions can seem overly complicated for simple storage tasks where SQL would be more apt.

Functional dependencies

Both languages address functional dependencies. SQL maintains data integrity through its constraint mechanisms, while Prolog uses its logic rules to represent dependencies and support various decision-making processes.

Logic fundamentals

A solid understanding of the first-order predicate calculus aids in mastering both SQL and Prolog. This provides the tools to unravel relational reasoning, the backbone of relational models in SQL and the facts-rules framework in Prolog.