Claude Skills by Intense-Visions

> Add new structure, migrate data, remove old structure -- the three-phase pattern for safe column renames, type changes, and table restructuring.

> How to read query execution plans to identify performance bottlenecks, row count misestimations, and missing indexes.

> Indexes on computed expressions and specialized index types (GIN, GiST) for non-scalar data like JSONB, arrays, and full-text search.

> Every column holds a single atomic value, no repeating groups exist, and every row is uniquely identifiable by a primary key.

> Modeling vertices and edges in SQL tables for social graphs, dependency networks, and recommendation systems with recursive queries -- and knowing when SQL stops being practical.

> Optimized for equality-only lookups with O(1) average access time, hash indexes are smaller than B-tree when range queries and ordering are never needed.

> Choosing between adjacency list, nested sets, closure table, and materialized path based on read/write ratio, query patterns, and tree depth.

> Distributing rows of a table across multiple database instances (shards) to scale beyond the capacity of a single server, with careful attention to shard key selection and cross-shard query complexity.

> The four SQL standard isolation levels control which concurrent transaction side-effects are visible, with PostgreSQL implementing them via MVCC snapshots rather than traditional locking.

> Selecting the right isolation level requires matching the workload's correctness requirements against the performance cost and retry complexity of stricter levels.

> Forward-only vs reversible migrations, data backfill safety, and blue-green schema patterns for confident schema evolution.

> MVCC allows readers and writers to operate concurrently without blocking each other by maintaining multiple versions of each row, with visibility determined by transaction snapshots.

> Encoding hierarchy position with left/right boundary numbers for O(1) subtree and ancestor queries at the cost of expensive writes.

> Optimistic locking assumes conflicts are rare, allows concurrent reads without locks, and detects conflicts at write time using version columns or conditional updates.

> Indexes with a WHERE clause that index only a subset of rows, reducing size and improving performance for targeted query patterns.

> Pessimistic locking acquires locks before modifying data, guaranteeing exclusive access and preventing conflicts at the cost of reduced concurrency.

> Modeling inheritance hierarchies and type-varying relationships in relational databases using single-table inheritance (STI), class-table inheritance (CTI), or shared foreign key patterns.

> Structural query transformations that help the planner choose better execution plans without changing results.

> How the planner uses table statistics (pg_stats, histograms, most-common-values) to estimate row counts and choose execution plans.

> The SQL standard defines three read anomalies (dirty, non-repeatable, phantom) that isolation levels progressively prevent, plus PostgreSQL adds write skew as a fourth anomaly relevant to Serializable.

> Understanding when the planner chooses sequential scan, index scan, bitmap scan, or index-only scan and why each is optimal for different selectivity ranges.

> Every non-key column must depend on the entire composite primary key, not just part of it -- eliminating partial dependencies.

> Splitting a large table into smaller physical partitions by range, list, or hash to improve query performance, simplify maintenance, and enable efficient data lifecycle management.

> Modeling when facts are true (valid-time), when they were recorded (transaction-time), or both (bitemporal), enabling time-travel queries and regulatory audit.

> "Every non-key attribute must provide a fact about the key, the whole key, and nothing but the key." -- Codd's memorable definition of full normalization through 3NF.

> Designing append-heavy tables for metrics, events, and logs with time-based partitioning, retention policies, and efficient aggregation.

> Splitting a wide table into multiple narrower tables, separating hot columns from cold columns, and managing large objects with TOAST to reduce I/O and improve cache efficiency.

> Online schema changes that avoid table locks and keep the application serving traffic throughout the migration.

> Perceived actionability — signifiers, constraints, mappings (Don Norman), flat design's affordance problem, touch targets, hover states as affordance

> Visual order through edge alignment, center alignment, optical alignment, and the invisible structure that consistent alignment creates across a page

> Apple's design philosophy covering clarity/deference/depth, vibrancy and material effects, SF Symbols integration, semantic color system, safe area management, and platform-specific navigation patterns across iOS, iPadOS, macOS, watchOS, and visionOS.

> Composition methodology for building design systems using five distinct levels of abstraction: atoms, molecules, organisms, templates, and pages.

> Visual coherence across every touchpoint — mapping brand attributes to design decisions, voice-to-visual translation, consistency vs. monotony, brand flex zones, and multi-platform coherence

> Color independence — conveying information without relying on color alone, building colorblind-safe palettes, and ensuring perceptual uniformity across all vision types

> Color wheel relationships — complementary, analogous, triadic, split-complementary, tetradic schemes with usage guidance for building cohesive palettes

> Emotional and cultural associations of color — warmth/coolness, trust, urgency, industry conventions, and cultural variance for global product design

> Anatomy of reusable components covering slots, variants, states, sizes, composition vs configuration, compound components, and when to split vs merge.

> Internal vs. external consistency — maintaining coherent patterns within a product, adhering to platform conventions, and knowing when to break consistency deliberately

> Information density as a deliberate design variable — compact, comfortable, and spacious modes, matching density to user context, and the tradeoff between showing more and showing clearly

> Luminance contrast for readability and visual weight — WCAG ratios, contrast as a hierarchy tool, contrast beyond accessibility

> Color adaptation for dark themes — inverted hierarchy, reduced saturation, elevation through lightness, surface layering, and maintaining brand identity in dark contexts

> Data visualization principles — chart type selection, color encoding, annotation strategy, Tufte's data-ink ratio, accessible charts, avoiding chartjunk, and small multiples for comparison

> Evaluating existing design — heuristic evaluation (Nielsen's 10), consistency inventory, accessibility audit, competitive analysis, identifying and quantifying design debt

> Structured feedback — critique frameworks (like/wish/wonder, what/why/improve), separating subjective preference from objective assessment, avoiding "I don't like it"

> Documenting design decisions — design rationale, spec handoff, annotating designs, living documentation, decision logs, the DESIGN.md format

> Living system maintenance covering contribution models, deprecation processes, versioning strategies, adoption metrics, and documentation standards for treating a design system as a product.

> Depth as information — shadow anatomy (offset, blur, spread, color), elevation scale, chromatic shadows, material metaphor, dark mode shadows

> Empty and error state design — empty states as onboarding, error states as recovery, 404 pages, zero-data states, degraded states, constructive error messages

> System response design — immediate vs delayed feedback, optimistic updates, progress indicators, confirmation patterns, undo vs confirm, toast/snackbar/banner

> Microsoft's cross-platform design system covering the five foundational elements (light, depth, motion, material, scale), Acrylic and Mica materials, reveal highlight interactions, connected animations, responsive container strategies, and the Fluent 2 token theming architecture.