I have the following table in my MariaDB database:

SQL table with WKT column

This table contains a column called 'coordinates' (type: LONGTEXT) with a wkt representation of either a MultiPolygon or a Polygon. I am attempting to convert this wkt representation to a type geom.

To do this, I tried running the following SQL Statements:

ALTER TABLE `database1`.`Federal_Info` ADD COLUMN `geom` Polygon;

UPDATE `database1`.`Federal_Info` SET geom =  ST_GeomFromText(coordinates, 4326);

However, I seem to be getting an error:

#1366 - Incorrect POLYGON value: 'MULTIPOLYGON' for column 'geom' at row 1

I also did try to see if there was anything wrong with the coordinates string, so I copied the entire string from the first row by executing the following command in sql:

SET @g= ST_GEOMFROMTEXT('MULTIPOLYGON (((-53.15910091775785 46.63184979843835, -53.15895811730544 46.63187509350104, ..., -53.96597790139074 47.43489159991098)))')

This code works without error so I'm incredibly confused why converting the column is causing a problem.

A bit of background to the table: I parsed a KML file, converted each of the coordinates to a Polygon Shapely object, and used the unary_union function to convert each Polygon into a MultiPolygon. From there I uploaded the dataframe (in Python) to my database.

1 Answer 1


You are trying to store a MultiPolygon in a Polygon (sized) column so it won't go.

Make your column a MultiPolygon column and then use st_multi to make any Polygons into MultiPolygons.

  • Thank you for the input. I realize I was trying to store a MultiPolygon into a Polygon column. So I changed the code to: ALTER TABLE `database1`.`Federal_Info` ADD COLUMN `geom` MultiPolygon; and from there I have to execute the following code: UPDATE `database1`.`Federal_Info` SET geom = ST_MULTI(ST_GeomFromText(coordinates, 4326));? or did I get this wrong? And this means that the only way I can do this is keep all my columns either MultiPolygons or Polygons, so it would be necessary to convert the Polygons to a MultiPolygon? Mar 17, 2022 at 16:56
  • Yes, that's right - usually you promote to multi if you need any of your geometries to be multi
    – Ian Turton
    Mar 17, 2022 at 17:09
  • thanks, I believe I understand. The thing is that since I am using MariaDB and not PostGIS, it says FUNCTION database1.ST_MULTI does not exist. I could split the two columns by adjusting my Python Code and keep two columns (one for MultiPolygon and one for Polygon). Would that be a better way? Mar 17, 2022 at 17:14
  • Two columns would be a nightmare for maintenance and performance - from a quick look at the Maria docs - try using MultiPolygon(poly1,poly2,...) on your polygons
    – Ian Turton
    Mar 18, 2022 at 8:34

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