Unlocking Spatial Relationships: Alternatives to WITHIN in MariaDB

WITHIN is a geometric function used within MariaDB's spatial extensions to determine the spatial relationship between two geometric objects. It's based on the original implementation in MySQL and employs object bounding rectangles for the comparison.

• Return Value
  
  • Returns 1 (TRUE) if geom1 is completely enclosed within geom2.
  • Returns 0 (FALSE) otherwise.
• Arguments
  
  • geom1: The first geometric object (e.g., a point, line, polygon).
  • geom2: The second geometric object to compare against.
• Function
  WITHIN(geom1, geom2)

Key Points

• For more precise spatial comparisons, MariaDB offers the ST_WITHIN function, which utilizes object shapes for a more accurate evaluation.
• It considers only the bounding boxes of the geometric objects, not their exact shapes. This can lead to inaccuracies for complex shapes.
• WITHIN is case-sensitive (e.g., Within and within are treated differently).

Example

SELECT *
FROM your_table
WHERE WITHIN(point_column, polygon_column) = 1;

This query would select rows from the your_table table where the point_column (representing a point) is entirely within the boundaries of the polygon_column (representing a polygon).

• For advanced spatial operations and more accurate results, consider using functions like ST_CONTAINS, ST_CROSSES, and others from the MariaDB spatial extension library.
• It's important to understand the limitations of bounding box-based comparisons when dealing with intricate shapes.
• WITHIN is primarily used with spatial data types like POINT, LINESTRING, and POLYGON.

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Example 1: Checking if a Point is Within a Square Polygon

This example checks if a point named my_point (latitude, longitude) falls within a square polygon defined by four corner points.

-- Define the square polygon (replace with your actual coordinates)
SET square_polygon = ST_GeomFromText('POLYGON((0 0, 10 0, 10 10, 0 10, 0 0))');

-- Check if the point is within the square
SELECT *
FROM your_table
WHERE WITHIN(my_point, square_polygon) = 1;

Example 2: Finding Stores Within a City Boundary

This example assumes you have tables for stores (with location point data) and a city boundary (city_boundary polygon).

SELECT store_name, address
FROM stores
WHERE WITHIN(location, city_boundary) = 1;

Important Note

Remember that WITHIN uses bounding boxes for comparison. If your polygons or shapes are complex, you might get inaccurate results. Consider using ST_WITHIN for more precise checks based on the actual shapes.

Additional Examples with ST_WITHIN (for reference)

Example 3 (Using ST_WITHIN): Checking if a Point is Within a Circle

SET circle_geom = ST_GeomFromText('POINT(5 5)');
SET my_point = ST_GeomFromText('POINT(3 7)');  -- Modify coordinates as needed

SELECT *
FROM your_table
WHERE ST_WITHIN(my_point, circle_geom) = 1;

This example utilizes ST_WITHIN to see if a point lies within the defined circle.

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ST_WITHIN

• Example:
• Syntax: ST_WITHIN(geom1, geom2)
• It uses the actual shapes of the geometries for comparison, leading to more precise results.
• This is the recommended alternative to "WITHIN".

SELECT *
FROM your_table
WHERE ST_WITHIN(point_column, polygon_column) = 1;

ST_CONTAINS

• Example:
• Syntax: ST_CONTAINS(geom1, geom2)
• Determines if one geometry completely contains another.

SELECT *
FROM your_table
WHERE ST_CONTAINS(polygon_column, point_column) = 1;  -- Check if polygon contains point

ST_INTERSECTS

• Example:
• Syntax: ST_INTERSECTS(geom1, geom2)
• Checks if two geometries have any part of their shapes overlapping.

SELECT *
FROM your_table
WHERE ST_INTERSECTS(line_column, polygon_column) = 1;  -- Check for line intersecting polygon

ST_DISJOINT

• Example:
• Syntax: ST_DISJOINT(geom1, geom2)
• Determines if two geometries have no intersection whatsoever.

SELECT *
FROM your_table
WHERE ST_DISJOINT(circle_column1, circle_column2) = 1;  -- Check if circles don't overlap

Choosing the Right Alternative

• For checking no overlap, use ST_DISJOINT.
• For overlaps, use ST_INTERSECTS.
• For containment checks, use ST_CONTAINS or ST_WITHIN (depending on direction).
• The best alternative depends on the specific spatial relationship you want to determine.

• Explore the extensive MariaDB spatial extension library for more advanced functions like ST_DWithin (distance within a tolerance), ST_Covers, and others.