ST_ToMultiLine() method

Converts the geometry to a multilinestring value.

Syntax

geometry-expression.ST_ToMultiLine()

Returns

ST_MultiLineString If the geometry-expression is of type ST_MultiLineString, returns the geometry-expression. If the geometry-expression is a geometry collection containing only lines, returns a multilinestring object containing the elements of the geometry-expression. If the geometry-expression is of type ST_LineString then return a multilinestring value containing one element, the geometry-expression. If the geometry-expression is the empty set, returns an empty set of type ST_MultiCurve. Otherwise, raises an exception condition.

Examples

Example 1 – The following returns an error because the Shape column is of type ST_Geometry and ST_Geometry does not support the ST_Length method.
```
SELECT Shape.ST_Length()
FROM SpatialShapes WHERE ShapeID = 29
```
The following uses ST_ToMultiLine to change the type of the Shape column expression to ST_MultiLineString. This example would also work with ShapeID 5, where the Shape value is of type ST_LineString. ST_Length returns the result 4.236068.
```
SELECT Shape.ST_ToMultiLine().ST_Length()
FROM SpatialShapes WHERE ShapeID = 29
```
In this case, the value of the Shape column is known be of type ST_MultiLineString, so TREAT can be used to efficiently change the type of the expression. This example would notwork with ShapeID 5, where the Shape value is of type ST_LineString. ST_Length returns the result 4.236068.
```
SELECT TREAT( Shape AS ST_MultiLineString ).ST_Length()
FROM SpatialShapes WHERE ShapeID = 29
```

Standards

SQL/MM (ISO/IEC 13249-3: 2006) 5.1.33