# How the POLYGON() function works in Mariadb?

The `POLYGON()`

function is a spatial function in Mariadb that creates a `Polygon`

object from a list of coordinates.

The `POLYGON()`

function is a spatial function in Mariadb that creates a `Polygon`

object from a list of coordinates. A `Polygon`

object is a closed shape that consists of a set of linear rings. A linear ring is a closed and simple line string that does not cross itself. The first linear ring of a `Polygon`

object is the exterior ring, and the subsequent ones are the interior rings or holes.

## Syntax

The syntax of the `POLYGON()`

function is as follows:

```
POLYGON(linestring1, linestring2, ...)
```

The function takes one or more arguments:

`linestring1`

: A`LineString`

object that represents the exterior ring of the polygon. The`LineString`

object can be created using the`LINESTRING()`

function or the`GeomFromText()`

function. The exterior ring must be defined in a counterclockwise direction, and the first and last points must be the same.`linestring2, ...`

: Optional`LineString`

objects that represent the interior rings or holes of the polygon. The`LineString`

objects can be created using the`LINESTRING()`

function or the`GeomFromText()`

function. The interior rings must be defined in a clockwise direction, and the first and last points must be the same.

The function returns a `Polygon`

object if the input is valid, otherwise it returns `NULL`

.

## Examples

### Example 1: Creating a simple polygon

The following example creates a simple polygon with four vertices and no holes from a list of coordinates.

```
SELECT POLYGON(LINESTRING(0 0, 0 10, 10 10, 10 0, 0 0)) AS polygon;
```

The output is a binary representation of the polygon object, which can be converted to a human-readable format using the `ST_AsText()`

function.

```
SELECT ST_AsText(POLYGON(LINESTRING(0 0, 0 10, 10 10, 10 0, 0 0))) AS polygon;
```

### Example 2: Creating a polygon with a hole

The following example creates a polygon with a hole from a list of coordinates. The hole is a smaller polygon inside the larger polygon.

```
SELECT POLYGON(LINESTRING(0 0, 0 10, 10 10, 10 0, 0 0), LINESTRING(2 2, 2 8, 8 8, 8 2, 2 2)) AS polygon;
```

The output can be converted to a human-readable format using the `ST_AsText()`

function.

```
SELECT ST_AsText(POLYGON(LINESTRING(0 0, 0 10, 10 10, 10 0, 0 0), LINESTRING(2 2, 2 8, 8 8, 8 2, 2 2))) AS polygon;
```

### Example 3: Creating a polygon with a specific SRID

The following example creates a polygon with a specific SRID of 4326, which corresponds to the WGS 84 coordinate system.

```
SELECT POLYGON(LINESTRING(0 0, 0 10, 10 10, 10 0, 0 0), 4326) AS polygon;
```

The output can be converted to a human-readable format using the `ST_AsText()`

function.

```
SELECT ST_AsText(POLYGON(LINESTRING(0 0, 0 10, 10 10, 10 0, 0 0), 4326)) AS polygon;
```

## Related Functions

There are some other functions that are related to the `POLYGON()`

function, such as:

`LINESTRING()`

: This function creates a`LineString`

object from a list of coordinates. A`LineString`

object is a one-dimensional shape that consists of a sequence of points. The syntax of the function is`LINESTRING(x1 y1, x2 y2, ...)`

, where`x1 y1, x2 y2, ...`

are the coordinates of the points.`GeomFromText()`

: This function creates a geometry object from a well-known text (WKT) representation. The WKT format is a text encoding of the spatial object. For example, the WKT representation of the polygon`POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))`

is`POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))`

. The syntax of the function is`GeomFromText(wkt, [srid])`

, where`wkt`

is a string and`srid`

is an optional integer.

## Conclusion

The `POLYGON()`

function is a useful function to create a `Polygon`

object from a list of coordinates. A `Polygon`

object is a closed shape that consists of a set of linear rings. The function takes one or more arguments, each of which is a `LineString`

object that represents a linear ring. The function returns a `Polygon`

object if the input is valid, otherwise it returns `NULL`

. The function can be used to perform spatial operations on polygons, such as calculating the area, perimeter, centroid, etc. The function can also be combined with other spatial functions, such as `ST_Contains()`

, `ST_Intersects()`

, `ST_Union()`

, etc., to perform spatial analysis and queries on polygons.