Aggregate functions supported by the Lindorm streaming engine -

Aggregate functions aggregate multiple Point or LineString objects into a single LineString object. This topic describes the spatio-temporal aggregate functions supported by the Lindorm streaming engine.

ST_MakeLine_Agg

Constructs a LineString object based on the specified Point or LineString column.

Syntax

geometry ST_MakeLine_Agg(geometry geom);

Parameters

Parameter	Description
geom	The specified geometry column.

Note

This function only supports columns of the Point or LineString type.
If you specify multiple LineString objects, duplicate nodes are deleted during the construction process.
If you specify multiple Point objects, duplicate nodes are not deleted.
This function constructs the LineString object only based on the data input order and does not sort data.

Examples

Example 1:
In this example, the data input order is from top to bottom.
id
name
geom
1
A
POINT (0 0)
2
B
POINT (0 1)
3
C
POINT (0 2)
Execute the following statement to construct a LineString object based on the geom column:
```
SELECT ST_AsText(ST_MakeLine_Agg(geom));
```
Sample output:
```
LINESTRING (0 0, 0 1, 0 2)
```
Example 2:
In this example, the data input order is from top to bottom.
id
name
geom
1
A
POINT (0 0)
3
C
POINT (0 2)
2
B
POINT (0 1)
Execute the following statement to construct a LindString object based on the geom column:
```
SELECT ST_AsText(ST_MakeLine_Agg(geom));
```
Sample output:
```
LINESTRING (0 0, 0 2, 0 1)
```

The returned results in Example 1 and Example 2 show that the ST_MakeLine_Agg function constructs the LineString object only based on the data input order and does not sort data.

ST_MakeLine_Ts_Agg

Constructs a LineString object based on the specified Point or LineString column and sorts data based on the timestamp column.

Syntax

geometry ST_MakeLine_Ts_Agg(geometry geom, timestamp ts)

Parameters

Parameter	Description
geom	The specified geometry column.
ts	The specified timestamp column.

Note

This function only supports columns of the Point or LineString type.
If you specify multiple LineString objects, duplicate nodes are deleted during the construction process.
If you specify multiple Point objects, duplicate nodes are not deleted.

Examples

Example 1:
In this example, the data input order is from top to bottom.
id
name
ts
geom
1
A
2022-01-01 10:00:00
POINT (0 0)
2
B
2022-01-01 10:00:03
POINT (0 1)
3
C
2022-01-01 10:00:02
POINT (0 2)
Execute the following statement to construct a LindString object based on the geom column and sort data based on the ts column:
```
SELECT ST_AsText(ST_MakeLine_Ts_Agg(geom,ts));
```
Sample output:
```
LINESTRING (0 0, 0 2, 0 1)
```
Example 2:
In this example, the data input order is from top to bottom.
id
name
ts
geom
1
A
2022-01-01 10:00:00
POINT (0 0)
3
C
2022-01-01 10:00:03
POINT (0 2)
2
B
2022-01-01 10:00:02
POINT (0 1)
Execute the following statement to construct a LindString object based on the geom column and sort data based on the ts column:
```
SELECT ST_AsText(ST_MakeLine_Ts_Agg(geom,ts));
```
Sample output:
```
LINESTRING (0 0, 0 1, 0 2)
```

id	name	ts	geom
1	A	2022-01-01 10:00:00	POINT (0 0)
2	B	2022-01-01 10:00:03	POINT (0 1)
3	C	2022-01-01 10:00:02	POINT (0 2)