docs/api/sql/box2d/Box2D-Functions/ST_Expand.md

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# ST_Expand

Introduction: Expand a `Box2D` outward by a per-axis or uniform delta. The expansion is applied symmetrically on each side (e.g., `dx = 1` widens the box by `1` on the left and `1` on the right). Negative deltas shrink the box; if they would invert it (`xmin > xmax` or `ymin > ymax`) the inverted box is returned as-is — callers can detect the degenerate result via the accessor functions.

This is the `Box2D` overload of [ST_Expand](../../Bounding-Box-Functions/ST_Expand.md), which also accepts a `Geometry`.

Format:

`ST_Expand(box: Box2D, uniformDelta: Double)`

`ST_Expand(box: Box2D, deltaX: Double, deltaY: Double)`

Return type: `Box2D`

Since: `v1.9.1`

SQL Example

```sql
SELECT ST_AsText(ST_Expand(ST_MakeBox2D(ST_Point(0.0, 0.0), ST_Point(10.0, 20.0)), 1.0))
```

Output:

```
BOX(-1.0 -1.0, 11.0 21.0)
```

Per-axis form:

```sql
SELECT ST_AsText(ST_Expand(ST_MakeBox2D(ST_Point(0.0, 0.0), ST_Point(10.0, 20.0)), 1.0, 2.0))
```

Output:

```
BOX(-1.0 -2.0, 11.0 22.0)
```

Returns `NULL` on `NULL` input.