Read a structured query — Alternative solution challenge

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

Compare two query plans as contracts

One plan filters stock then projects id/name/stock. Another projects those same fields then filters stock. Supplied rows all contain numeric stock.

For these rows both plans can produce the same values because stock remains available for filtering. If projection removed stock first, the second plan could not apply its predicate without another contract. Equivalent outputs do not imply identical performance or host implementation.

Write the intermediate states explicitly before proposing a code change. The example below remains an illustrative source anchor; this new case changes the inputs or the host requirement. WillowScript and these library services are proposed and unimplemented here. Treat new policies as supplied exercise contracts, and keep hand predictions distinct from native execution evidence.

Worked reasoning and supplied artifact

// PAPER FIXTURE — Compare two query plans as contracts
// Manual worked artifact; comments below are not executable source.
// INPUT / CONTRACT: One plan filters stock then projects id/name/stock. Another projects those same fields
// then filters stock. Supplied rows all contain numeric stock.
// DERIVATION / EXPECTED ARTIFACT: For these rows both plans can produce the same values because stock
// remains available for filtering. If projection removed stock first, the second plan could not apply its
// predicate without another contract. Equivalent outputs do not imply identical performance or host
// implementation.

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 both plans on four rows, then remove stock from the early projection and explain the missing dependency.

What to produce

Trace both plans on four rows, then remove stock from the early projection and explain the missing dependency.

• 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.

• Compare two query plans as contracts
• One plan filters stock then projects id/name/stock. Another projects those same fields then filters stock. Supplied rows all contain numeric stock.
• Separate source-backed behavior, host requirements and untested predictions.

One small recap task

Change one input in this case and state which intermediate state or calculation must be recomputed. Explain why “Projection automatically recreates missing fields” is not justified.

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