Read a structured query — Discover and trace

PART I

Warm-up

Reconnect with a useful idea before starting read a structured query. In one or two sentences, describe the input, output or host boundary from the previous exercise that this lesson builds on. If you are arriving directly, skim the worked example first; there is no locked prerequisite.

A rough note is enough. You can revise it after the example.

PART II

Instruction & guided example

Trace a query over supplied rows

Exercise host supplies products rows A=(Apple,0), B=(Bolt,9), C=(Cable,10), D=(Drill,3). The source’s WDB example selects id/name/stock, filters stock < 10 and orders by stock.

Filter first: A, B and D qualify; C is excluded at equality. Ascending order gives A(0), D(3), B(9). Projection retains only the named fields. These are hand-traced results from the supplied table, not a query against this website’s SQLite database. An import does not create products or grant permission to read it.

Use the supplied case as a paper design exercise. WillowScript and these library integrations are proposed and unimplemented here; no interpreter or native host has checked the example. Preserve the source API spellings, label new policies as exercise-host contracts, and distinguish a predicted result from measured execution.

Worked reasoning and supplied artifact

// PAPER FIXTURE — Trace a query over supplied rows
// Manual worked artifact; comments below are not executable source.
// INPUT / CONTRACT: Exercise host supplies products rows A=(Apple,0), B=(Bolt,9), C=(Cable,10),
// D=(Drill,3). The source’s WDB example selects id/name/stock, filters stock < 10 and orders by stock.
// DERIVATION / EXPECTED ARTIFACT: Filter first: A, B and D qualify; C is excluded at equality. Ascending
// order gives A(0), D(3), B(9). Projection retains only the named fields. These are hand-traced results
// from the supplied table, not a query against this website’s SQLite database. An import does not create
// products or grant permission to read it.

Illustrative example from the proposed WillowScript design. The language and WUIX/WMATH/WDB/WAUDIO/WTMP services are not implemented in the supplied source. This site has no interpreter, VM or native host and does not execute or certify the snippet.

Try the guided change

Reconstruct the supplied worked case first: list its inputs, intermediate decisions and final artifact. Compare each row with the explanation and identify exactly where the rejected alternative fails. Then use the changed inputs in Part IV for independent work.

• Write the supplied inputs and initial state before following the example.
• Reconstruct each intermediate calculation or host decision, then compare with the worked artifact.
• Explain why the contrasting alternative fails before attempting the changed inputs in Part IV.

PART III

Take a breather

Step back after the guided example. Look away from the screen, stretch, or reread your prediction. This is an optional learning pause, not a timer or an assessment gate.

When you return, try to name the lesson’s key idea without copying its wording. If that feels difficult, return to Part II and trace one line rather than restarting the entire lesson.

PART IV

Independent practice

Project context: Inventory review workspace. Build a small, understandable change around read a structured query.

Trace rows E=12, F=1 and G=9 with names you choose. Produce the exact selected fields in expected order.

What to produce

Trace rows E=12, F=1 and G=9 with names you choose. Produce the exact selected fields in expected order.

• State the intended behavior in a sentence before editing.
• Use only source-backed syntax and the host services whose contract you have been given.
• Record a normal case and a boundary or unavailable-resource case.
• Label hand predictions separately from anything actually measured in a supplied toolchain.

Syntax colors are a reading aid, not a compiler. The line you are editing stays uncolored until you move to a different line; capitalization is never changed. Drafts stay on this browser and code is not executed.

import wdb;
domain Inventory {
    const lowStock = wdb.query({
        from: products,
        select: [id, name, stock],
        where: [[ stock < 10 ]],
        order: { by: stock, direction: ascending }
    });
}

PART V

Self-check

Use this check to notice what to revisit. It does not award a private course grade, block another page or claim to verify compiled code. Every answer has a learning explanation.

You may keep exploring even if you are unsure. Use the hint, compare the trace, and revise your explanation.

PART VI

Recap & small task

Bring the idea back to the mod feature you are building. A useful recap connects the mechanism to a decision you can make in your own code.

• Trace a query over supplied rows
• Exercise host supplies products rows A=(Apple,0), B=(Bolt,9), C=(Cable,10), D=(Drill,3). The source’s WDB example selects id/name/stock, filters stock < 10 and orders by stock.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Explain why “A with stock 0” fails for the supplied case, then give one changed input that would require revisiting your conclusion.

This marks your personal practice record only. It is not a certification or an official workspace assessment.