<->
功能描述
计算对象之间的距离。
适用于POINT与另一种几何类型的所有组合，以及这些额外的类型对：(BOX, LSEG)，(BOX, LINE)，(LSEG, LINE)，(POLYGON, CIRCLE)，以及易子情况。
数据类型
| L_OPERAND_TYP（左操作数类型） | R_OPERAND_TYP（右操作数类型） | RET_TYPE（返回类型） |
|---|---|---|
| POINT | POINT | DOUBLE |
| POINT | BOX | |
| POINT | LSEG | |
| POINT | LINE | |
| POINT | PATH | |
| POINT | POLYGON | |
| POINT | CIRCLE | |
| BOX | POINT | |
| BOX | BOX | |
| BOX | LSEG | |
| LINE | POINT | |
| LINE | LSEG | |
| LINE | LINE | |
| LSEG | POINT | |
| LSEG | BOX | |
| LSEG | LSEG | |
| LSEG | LINE | |
| POLYGON | POINT | |
| POLYGON | POLYGON | |
| POLYGON | CIRCLE | |
| PATH | POINT | |
| PATH | PATH | |
| CIRCLE | POINT | |
| CIRCLE | POLYGON | |
| CIRCLE | CIRCLE |
示例
计算圆到圆的距离
sqlSQL> SELECT CIRCLE('<(0,0),1>') <-> CIRCLE('<(5,0),1>'); EXPR1 | ------------------------------------------------------------------------------ 3.000000e+00 | Total 1 records.计算点到线段的距离
sqlSQL> SELECT POINT('(0,0)') <-> LSEG('[(2,0),(0,2)]') ; EXPR1 | ------------------------------------------------------------------------------ 1.414214e+00 | Total 1 records.计算圆到多边形的距离
sqlSQL> SELECT CIRCLE('<(0,0),1>') <-> POLYGON('( 10, 110, 20, 120, 30, 130, 40, 140)'); EXPR1 | ------------------------------------------------------------------------------ 1.094536e+02 | Total 1 records.