Considerations and associated data types for spatial functions

This section provides information that you need to know when you code spatial functions.

This information includes:

Factors to consider: the requirement to specify the schema to which spatial functions belong, and the fact that some functions can be invoked as methods.
How to address a situation in which a spatial function cannot process the type of geometries returned by another spatial function.
A table showing which functions take values of each spatial data type as input

When you use spatial functions, be aware of these factors:

Before a spatial function can be called, its name must be qualified by the name of the schema to which spatial functions belong: DB2GSE. One way to do this is to explicitly specify the schema in the SQL statement that references the function; for example:
```
SELECT db2gse.ST_Relate (g1, g2, 'T*F**FFF2') EQUALS FROM relate_test
```
Alternatively, to avoid specifying the schema each time a function is to be called, you can add DB2GSE to the CURRENT FUNCTION PATH special register. To obtain the current settings for this special register, type the following SQL command:
```
VALUES CURRENT FUNCTION PATH
```
To update the CURRENT FUNCTION PATH special register with DB2GSE, issue the following SQL command:
```
set CURRENT FUNCTION PATH = CURRENT FUNCTION PATH, db2gse
```
Some spatial functions can be invoked as methods. In the following code, for example, ST_Area is invoked first as a function and then as a method. In both cases, ST_Area is coded to operate on a polygon that has an ID of 10 and that is stored in the SALES_ZONE column of a table named STORES. When invoked, ST_Area will return the area of the real-world feature-Sales Zone no. 10-that the polygon represents.
ST_Area invoked as a function:
```
SELECT ST_Area(sales_zone)
FROM   stores
WHERE  id = 10 
```
ST_Area invoked as a method:
```
SELECT sales_zone..ST_Area()
FROM   stores
WHERE  id = 10 
```

The functions ST_BuildMBRAggr and ST_BuildUnionAggr are described in "MBR Aggregate" and "Union Aggregate", respectively.