SQL

Pivot Without PIVOT (Conditional Aggregation)

Most databases don't have a real `PIVOT` keyword (SQL Server does). The portable answer is conditional aggregation — `SUM(CASE WHEN ...) AS col` for each pivoted value.

1h ago 0

Rust

Async/Await with tokio

`async fn` returns a future; `.await` drives it. tokio is the de-facto runtime. The `#[tokio::main]` attribute turns `main` into the runtime entry point.

1h ago 0

HTML

Video Element with Captions

`<video>` with multiple `<source>` formats (MP4 + WebM), `controls`, `poster`, and a captions track via `<track kind="captions">`. All shipped with the browser — no JS player needed.

1h ago 0

TypeScript

URL Builder with Type-Safe Query

Build URLs with a clean query-param API. Skips null/undefined automatically, encodes everything, and accepts arrays for repeated keys. Avoids manual string concatenation.

1h ago 0

Kotlin

kotlin.test — Basic Tests

`kotlin.test` is the multiplatform test stdlib. `@Test` marks a test; `assertEquals`, `assertTrue`, `assertFailsWith` are the workhorses.

1h ago 0

Python

asyncio.to_thread — Run Blocking Code

Wrap a blocking function so it doesn't freeze the event loop. asyncio.to_thread (3.9+) schedules the call onto the default executor and awaits the result.

1h ago 0

Kotlin

Star Projections (List<*>, etc.)

`List<*>` means "list of something I don't need to know exactly" — read-only with Any? as element type. Useful when you genuinely don't care about the parameter.

1h ago 0

Rust

Serde — Derive Serialize / Deserialize

`#[derive(Serialize, Deserialize)]` is the one-liner that bridges Rust structs and JSON / YAML / TOML / etc. via serde's data-format crates.

1h ago 0

PHP

Average / Median / Mode

Three classic descriptive statistics over a numeric array. Built without any external math library — just sort + count.

1h ago 0

SQL

FIRST_VALUE / LAST_VALUE

Return the first or last value within a window. Useful for "compare each row to the partition's first/last value" — for example, "how much have we grown since the user's first order?"

1h ago 0

Java

AtomicInteger / LongAdder

Lock-free atomics for shared counters. `AtomicInteger` for low contention; `LongAdder` for high contention (shards internally — much faster under heavy parallel load).

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Kotlin

Ktor Client — POST JSON with Serialization

Combine Ktor + kotlinx.serialization: register the JSON plugin, declare `@Serializable` data classes, the client (de)serializes automatically.

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Rust

reqwest GET + JSON Deserialize

`reqwest` is the standard HTTP client. Combined with serde, you can fetch and parse a JSON API response into a typed struct in three lines.

1h ago 0

Python

pairwise — Rolling Pair Iterator

`pairwise([a, b, c, d])` yields `(a, b), (b, c), (c, d)` — built into itertools since 3.10. Perfect for "diff consecutive elements" patterns (deltas, rate-of-change, validation between rows).

1h ago 0

SQL

Sessionization — Group Events into Sessions

Stitch a stream of events into "sessions" where events more than N minutes apart start a new session. Uses LAG + a SUM-OVER trick to assign session IDs.

1h ago 0

PHP

Validate Hex Color

Accept #RGB, #RGBA, #RRGGBB, or #RRGGBBAA hex colors (with or without the leading #). Returns the normalized 6/8-digit lowercase form.

1h ago 0

PHP

Slack Incoming-Webhook Notification

Fire a quick notification to a Slack channel via an incoming webhook URL. Includes basic markdown-style mentions and an attachment color for severity.

1h ago 0

SQL

NULLS FIRST / NULLS LAST

Control where NULLs land in an `ORDER BY`. PostgreSQL/Oracle default NULLs to LAST in ASC, FIRST in DESC; MySQL/SQL Server flip it. Be explicit if it matters.

1h ago 0

SQL

Views and Materialized Views

A view is a named query — no data stored. A materialized view caches the result; refresh it on demand. Great for expensive joins or aggregations that don't need to be real-time.

1h ago 0

Rust

Clone vs Copy — When to Use Each

Stack-allocated primitives implement `Copy` (auto-duplicated). Heap-owning types like `String` and `Vec` only implement `Clone` (you must explicitly call `.clone()` to opt into the deep copy cost).

1h ago 0

SQL

STRING_AGG / GROUP_CONCAT

Concatenate values across a group into a single delimited string. PostgreSQL/MSSQL use `STRING_AGG`; MySQL uses `GROUP_CONCAT`; SQLite has both.

1h ago 0

SQL

Gap Detection — Missing Days / Sequences

Find holes in a series — missing invoice numbers, days with no events, gaps in a sequence. Combine `LAG` (or `generate_series`) with a join to spot them.

1h ago 0

Rust

Arc<Mutex<T>> — Shared Mutable State

Share mutable data across threads: `Arc` for the shared ownership, `Mutex` for the synchronized access. Lock with `.lock().unwrap()`; the guard drops the lock on scope exit.

1h ago 0

Bash

Sort by a Specific Column

Sort takes -k for column-based ordering and -t to set the delimiter. -h sorts human-readable sizes ("1.5G", "300K") correctly.

1h ago 0

Kotlin

also — Side Effect, Return Itself

`x.also { ... }` runs a side-effect block with `x` as `it` and returns `x` unchanged. Used for logging, debugging, or asserting mid-chain without breaking it.

1h ago 0

Python

Literal + match for Exhaustive Switching

`Literal` pins a value to specific strings/ints. Combine with the match statement (Python 3.10+) and a `_ : assert_never` clause for exhaustiveness — every variant must be handled or mypy yells at you.

1h ago 0

SQL

Moving Average (Window Frame)

Add a frame clause (`ROWS BETWEEN N PRECEDING AND CURRENT ROW`) to compute moving averages, sliding sums, rolling stats — anything that needs a bounded look-back.

1h ago 0

Python

asyncio.wait_for — Timeout Wrapper

Cancel a coroutine if it takes longer than `timeout` seconds. Raises asyncio.TimeoutError when fired so the caller can fall back. Python 3.11+ has asyncio.timeout() as a context-manager alternative.

1h ago 0

HTML

Figure + Figcaption (Images, Code, Charts)

`<figure>` groups self-contained illustrative content with its caption. Use it for images, code blocks, charts, diagrams — anything that's referenced from the surrounding text but stands on its own.

1h ago 0

Rust

zip / enumerate / chain

Three adapters that pair, index, and concatenate iterators. Every Rust developer reaches for them daily.

1h ago 0