ST_ISVALID¶

语法¶

ST_ISVALID( <geography_or_geometry_expression> )

实参¶

geography_or_geometry_expression

实参必须是 GEOGRAPHY 或 GEOMETRY 类型的表达式。

返回¶

返回 BOOLEAN。

使用说明¶

• ST_ISVALID only checks for the validity of a shape. It doesn't modify data. When constructing objects from spatial formats (such as WKT, WKB, EWKT, EWKB, or GeoJSON), conversion functions (for example, TO_GEOGRAPHY, TO_GEOMETRY, ST_GEOGRAPHYFROMWKT, or ST_GEOMETRYFROMWKT) parse input and by default attempt to validate or repair shapes. If a conversion function can't repair a shape, it returns an error unless you accept invalid shapes.

• To ingest data that might be invalid (for example, data that you plan to correct later), specify TRUE for the additional allow_invalid argument when you call the conversion function to allow an invalid shape. You can then use the ST_ISVALID function to flag invalid rows in a table.

• Some geospatial functions might return an error or unusable results when given invalid shapes. Use the ST_ISVALID function to check validity. You can correct invalid shapes before performing spatial analytics.

• When shapes are invalid, simple corrections include buffering with a small positive or negative distance (for example, to remove tiny spikes or resolve self-intersections) and then rechecking validity using the ST_ISVALID function.

示例¶

The following examples use the ST_ISVALID function.

Determine whether a polygon is a valid shape:

SELECT ST_ISVALID(
    TO_GEOGRAPHY('POLYGON((-93.086 37.557,-86.699 37.497,-93.198 35.123,-93.086 37.557))')
  ) AS is_valid;

+----------+
| IS_VALID |
|----------|
| True     |
+----------+

SELECT ST_ISVALID(
    TO_GEOGRAPHY( 'POLYGON((-92.799 37.601,-88.240 37.617,-92.733 36.198,-88.305 36.171,-92.799 37.601))', TRUE)
  ) AS is_valid;

+----------+
| IS_VALID |
|----------|
| False    |
+----------+

Correct an invalid shape by using the ST_BUFFER function to add small buffer:

WITH g AS (
  SELECT TO_GEOMETRY('POLYGON((0 0, 2 2, 2 0, 0 2, 0 0))', TRUE) AS geom
)
SELECT ST_ISVALID(geom) AS is_valid_before_buffer,
  ST_ISVALID(ST_BUFFER(geom, -0.001)) AS is_valid_after_buffer
  FROM g;

+------------------------+-----------------------+
| IS_VALID_BEFORE_BUFFER | IS_VALID_AFTER_BUFFER |
|------------------------+-----------------------|
| False                  | True                  |
+------------------------+-----------------------+