Categories:: Geospatial functions

ST_COLLECT¶

There are two forms of ST_COLLECT:

Scalar: This function combines two GEOGRAPHY objects into one.
Aggregate: This function combines all the GEOGRAPHY objects in a column into one GEOGRAPHY object.

Syntax¶

Scalar:

    ST_COLLECT( <geography_expression_1> , <geography_expression_2> )

Aggregate:

    ST_COLLECT( <geography_expression_1> )

Arguments¶

geography_expression_1: A GEOGRAPHY object.
geography_expression_2: A GEOGRAPHY object.

Returns¶

The function returns a value of type GEOGRAPHY.

Usage notes¶

If g1 and g2 are both Point objects, the result is a MultiPoint object containing the two Points. Similarly, if g1 and g2 are both LineString objects, the result is a MultiLineString object. Etc.
If g1 and g2 are different types of geospatial objects, or if at least one of the input GEOGRAPHY objects is a collection (e.g. MultiLineString, GeometryCollection, or FeatureCollection), then the result is a GeometryCollection containing both input objects.

Examples¶

The queries below show both scalar and aggregate uses of the ST_COLLECT function.

Create and load the table:

CREATE TABLE geo3 (g1 GEOGRAPHY, g2 GEOGRAPHY);
INSERT INTO geo3 (g1, g2) VALUES
    ( 'POINT(-180 -90)', 'POINT(-45 -45)' ),
    ( 'POINT(   0   0)', 'POINT(-60 -60)' ),
    ( 'POINT(+180 +90)', 'POINT(+45 +45)' );

This calls ST_COLLECT as a scalar function to create a MultiPoint value that contains both points in the same row:

-- Scalar function:
SELECT ST_COLLECT(g1, g2) FROM geo3;
+------------------------+
| ST_COLLECT(G1, G2)     |
|------------------------|
| {                      |
|   "coordinates": [     |
|     [                  |
|       -180,            |
|       -90              |
|     ],                 |
|     [                  |
|       -45,             |
|       -45              |
|     ]                  |
|   ],                   |
|   "type": "MultiPoint" |
| }                      |
| {                      |
|   "coordinates": [     |
|     [                  |
|       0,               |
|       0                |
|     ],                 |
|     [                  |
|       -60,             |
|       -60              |
|     ]                  |
|   ],                   |
|   "type": "MultiPoint" |
| }                      |
| {                      |
|   "coordinates": [     |
|     [                  |
|       180,             |
|       90               |
|     ],                 |
|     [                  |
|       45,              |
|       45               |
|     ]                  |
|   ],                   |
|   "type": "MultiPoint" |
| }                      |
+------------------------+

This calls ST_COLLECT as an aggregate function to create a MultiPoint value that contains all the points in the same column:

-- Aggregate function:
SELECT ST_COLLECT(g1), ST_COLLECT(g2) FROM geo3;
+------------------------+------------------------+
| ST_COLLECT(G1)         | ST_COLLECT(G2)         |
|------------------------+------------------------|
| {                      | {                      |
|   "coordinates": [     |   "coordinates": [     |
|     [                  |     [                  |
|       -180,            |       -45,             |
|       -90              |       -45              |
|     ],                 |     ],                 |
|     [                  |     [                  |
|       0,               |       -60,             |
|       0                |       -60              |
|     ],                 |     ],                 |
|     [                  |     [                  |
|       180,             |       45,              |
|       90               |       45               |
|     ]                  |     ]                  |
|   ],                   |   ],                   |
|   "type": "MultiPoint" |   "type": "MultiPoint" |
| }                      | }                      |
+------------------------+------------------------+

This calls ST_COLLECT first as an aggregate function on each column to create MultiPoint values that contains all the points in each column, and then calls ST_COLLECT on those two MultiPoint values to create a GeometryCollection that contains all the points in both columns. The resulting GeometryCollection is hierarchical.

-- Aggregate and then Collect:
SELECT ST_COLLECT(ST_COLLECT(g1), ST_COLLECT(g2)) FROM geo3;
+--------------------------------------------+
| ST_COLLECT(ST_COLLECT(G1), ST_COLLECT(G2)) |
|--------------------------------------------|
| {                                          |
|   "geometries": [                          |
|     {                                      |
|       "coordinates": [                     |
|         [                                  |
|           -180,                            |
|           -90                              |
|         ],                                 |
|         [                                  |
|           0,                               |
|           0                                |
|         ],                                 |
|         [                                  |
|           180,                             |
|           90                               |
|         ]                                  |
|       ],                                   |
|       "type": "MultiPoint"                 |
|     },                                     |
|     {                                      |
|       "coordinates": [                     |
|         [                                  |
|           -45,                             |
|           -45                              |
|         ],                                 |
|         [                                  |
|           -60,                             |
|           -60                              |
|         ],                                 |
|         [                                  |
|           45,                              |
|           45                               |
|         ]                                  |
|       ],                                   |
|       "type": "MultiPoint"                 |
|     }                                      |
|   ],                                       |
|   "type": "GeometryCollection"             |
| }                                          |
+--------------------------------------------+