This topic describes GiST indexing. You can create a GiST index on the column that stores trajectory data.
Syntax
CREATE INDEX [index_name] on table_name USING GIST(traj_col [operator_family]);- index_name: the name of the index. This parameter is optional.
- table_name: the name of the table to which the column belongs.
- traj_col: the name of the column.
- operator_family: the operator family that is used to create the index. Default value: trajgist_ops_3dt. This parameter is optional.
Note The created index accelerates queries that are run by operators and the following
functions: ST_ndIntersect, ST_ndDWithin, ST_ndContains, and ST_ndWithin.
Supported operator families
The following table describes the operator families that are supported by GiST.
| Operator family | Description |
|---|---|
| trajgist_ops_z | Creates an index on the z axis. This type of index supports queries that cover only the z axis. |
| trajgist_ops_t | Creates an index on the t axis. This type of index supports queries that cover only the t axis. |
| trajgist_ops_2d | Creates an index on the x and y axes. This type of index supports queries that cover only the x and y axes. |
| trajgist_ops_2dt | Creates an index on the x, y, and t axes. This type of index supports queries that cover only the x and y axes, queries that cover only the t axis, and queries that cover the x, y, and t axes. |
| trajgist_ops_3d | Creates an index on the x, y, and z axes. This type of index supports queries that cover only the x and y axes, queries that cover only the z axis, and queries that cover the x, y, and z axes. |
| trajgist_ops_3dt | Creates an index on the x, y, z, and t axes. This type of index supports all of the queries that are supported by the preceding five operator families. |
Note In most cases, a smaller number of dimensions in the created index indicates a higher
speed per query. If you frequently run a specific type of query, we recommend that
you specify another operator family that meets your dimension requirements in addition
to the default trajgist_ops_3dt operator family.
Example
-- Create an index on the t axis.
CREATE INDEX on table_name USING GIST(traj_col trajgist_ops_t);
-- Create an index on the x and y axes.
CREATE INDEX on table_name USING GIST(traj_col trajgist_ops_2d);
-- Create an index on the x, y, and t axes.
CREATE INDEX on table_name USING GIST(traj_col trajgist_ops_2dt);