science

PL/Perl

PL/Perl is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand PL/Perl rather than just read about it. In short: PL/Perl (Procedural Language/Perl) is a procedural language supported by the PostgreSQL RDBMS. PL/Perl, as an imperative programming language, allows more control than the relational algebra of SQL.

Key takeaways

PL/Perl belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PL/Perl to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PL/Perl from memory before moving on to harder problems.

Reference excerpt

PL/Perl (Procedural Language/Perl) is a procedural language supported by the PostgreSQL RDBMS. PL/Perl, as an imperative programming language, allows more control than the relational algebra of SQL. Programs created in the PL/Perl language are called functions and can use most of the features that the Perl programming language provides, including common flow control structures and syntax that has incorporated regular expressions directly. These functions can be evaluated as part of a SQL statement, or in response to a trigger or rule. The design goals of PL/Perl were to create a loadable procedural language that:

can be used to create functions and trigger procedures, adds control structures to the SQL language, can perform complex computations, can be defined to be either trusted or untrusted by the server, is easy to use. PL/Perl is one of many "PL" languages available for PostgreSQL PL/pgSQL PL/Java, plPHP, PL/Python, PL/R, PL/Ruby, PL/sh, and PL/Tcl.

References PostgreSQL PL/Perl documentation

Worked examples

Example 1 — a first encounter with PL/Perl

Start with the simplest possible case. Write down what PL/Perl claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PL/Perl before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PL/Perl ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PL/Perl

In research: PL/Perl appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses PL/Perl in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: PL/Perl is common in secondary-school and first-year university syllabi. It links to neighbouring topics Data-centric programming languages, Data management, PostgreSQL, so understanding it makes those chapters shorter.
In everyday life: Look for PL/Perl outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study PL/Perl in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PL/Perl means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain PL/Perl out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PL/Perl in simple terms?

PL/Perl (Procedural Language/Perl) is a procedural language supported by the PostgreSQL RDBMS. PL/Perl, as an imperative programming language, allows more control than the relational algebra of SQL.

Why does PL/Perl matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PL/Perl?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PL/Perl.