https://dailypypy.org/tags/data-contracts/ Recent content in Data-Contracts on 每日拍拍 Hugo -- gohugo.io zh-tw © 2026 每日拍拍 Thu, 22 Oct 2026 11:14:00 +0800 155076163427069952 154825760438254592 https://dailypypy.org/learn/polars-join-cardinality-validation/ Thu, 22 Oct 2026 11:14:00 +0800 https://dailypypy.org/learn/polars-join-cardinality-validation/ <!--- 1440x768 prompt: masterpiece, best quality, highres, clean anime illustration, japanese anime style, soft shading, flat color design, 1girl, black hair, green eyes, white off-shoulder shirt, black short skirt, three-quarter cowboy shot with slight dutch angle, standing with one hand gently touching her chin and the other resting on her hip, inquisitive thoughtful closed-mouth smile, looking at viewer, pastel pale apricot background, neat composition, detailed eyes, cute and smart vibe, minimal background, polished illustration, no text negative prompt: worst quality, bad eye, bad hand, extra limbs, manga, multiple views, monochrome, text, signature dedup note: Focused relational-contract follow-up to ../python-polars/. ../pandas-data-cleaning/ has one many_to_one merge example; this is not its Polars translation. This article centers composite-key identity, multiplicative cardinality, explicit null policy, bidirectional anti-join reconciliation, matched-versus-null-attribute provenance, fail-closed enrichment and negative fixtures. ../polars-nested-json-ndjson/ owns nested expansion; ../polars-lazyframe-query-optimization/ owns execution plans. Strict 198-post current-source inventory checked before drafting. source check: Official Polars DataFrame.join API and join guide reviewed 2026-10-22; executable examples target Python 3.12 / Polars 2.0.0. Policies below are fictional application contracts, not universal customer-data rules. verification: Eight Python blocks parsed and sequential demo passed; 33 pytest cases passed on Python 3.12 / Polars 2.0.0, including native cardinality modes, Null policy, composite-key scope, empty inputs, schema drift and fail-closed gate. Current-source maximum character 5-gram Jaccard 0.066691 versus nested JSON; manual review confirms distinct relation-contract scope. Cover prompt 17999725-bcd3-448f-9cc0-0a44a1df08c2 produced DAILYPYPY_00143_.png, PNG 1440x768 verified and visually inspected for text, face, hands and artifacts. publication note: date keeps the required random 10:00–13:00 time; publishDate permits the scheduled morning release with buildFuture=false. ---> <h2 class="relative group">一. 前言：Join 沒報錯，營收卻變多了 <div id="一-前言join-沒報錯營收卻變多了" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 ltr:-left-6 rtl:-right-6 not-prose group-hover:opacity-100"> <a class="group-hover:text-primary-300 dark:group-hover:text-neutral-700" style="text-decoration-line: none !important;" href="#%e4%b8%80-%e5%89%8d%e8%a8%80join-%e6%b2%92%e5%a0%b1%e9%8c%af%e7%87%9f%e6%94%b6%e5%8d%bb%e8%ae%8a%e5%a4%9a%e4%ba%86" aria-label="定位點">#</a> </span> </h2> <p>嗨，我是拍拍君。今天的任務很單純：替訂單補上客戶名稱。 五筆訂單進去，七筆資料出來，程式還笑咪咪地正常結束。 不是業績突然變好，是右表同一個客戶出現兩次。</p>