# Query Types

AQL provides several query classes that form a hierarchy of capabilities. Each class encapsulates a different aspect of database interactions, from full table access down to individual value manipulation.

## Query Type Hierarchy

All query types inherit from `StagedObject`, which records operations as a pipeline of stages. The hierarchy is:

```
Query<T>
├── Datum<T>
│   └── SingleSelection<T>
└── Stream<T>
    └── Selection<T>
        └── Table<T>

ValueProxy<T> (used within query callbacks)
```

## Common Features

All query types that extend `Query<T>` share these capabilities:

- **`run()`** - Execute the query and return a `Promise<T>` with the result.
- **`then()`** - `PromiseLike` support, so queries can be awaited directly.
- **`cursor()`** - Return an `AsyncGenerator` for streaming results one at a time.
- **`[Symbol.asyncIterator]()`** - Enable `for await...of` loops over query results.

```typescript
import { Schema } from "@antelopejs/interface-database";

// Execute a query explicitly
const result = await schema.instance().table("users").run();

// Await the query directly (uses PromiseLike)
const users = await schema.instance().table("users");

// Iterate with async generator
for await (const user of schema.instance().table("users")) {
  console.log(user.name);
}
```

## Available Query Types

- [**Table**](./2.table.md) - Represents a database table with insert, get, getAll, and between operations
- [**Selection**](./3.selection.md) - A set of documents supporting update, replace, and delete
- [**SingleSelection**](./4.single_selection.md) - A single document with update, replace, delete, and change feed support
- [**Stream**](./5.stream.md) - A sequence of results with map, filter, join, group, aggregate, and sort operations
- [**Change Feeds**](./6.feed.md) - Real-time change notifications via the `changes()` method
- [**Query**](./7.query.md) - The base class providing execution and async iteration
- [**Datum**](./8.datum.md) - A single value with field access, transformation, and lookup capabilities
- [**ValueProxy**](./9.valueproxy.md) - Proxy for in-query value operations (arithmetic, string, date, array, object)