first()/last()

Function Description

cmp_col is used for comparison to return the value of the column specified by the first or last value. The first and last operators in the timeseries_catalog schema is different from those in the public schema.

Syntax

select city_name,timeseries_catalog.first(temp_c,time) from weather_metrics group by city_name;
select city_name,timeseries_catalog.last(temp_c,time) from weather_metrics group by city_name;
timeseries_catalog.first(value, cmp_col)
timeseries_catalog.last(value, cmp_col)

Parameter Description

Constraints

If there are same minimum or maximum values in the cmp_col column, return the first or last value.

If the values in the cmp_col column are constants, the first and last operators equal those in the public schema, and the first or last value will be returned.

Examples

Uqbar=# select city_name,timeseries_catalog.first(temp_c,time) from weather_metrics group by city_name; 
 city_name | first 
---------------+-------
beijing    | 30
shanghai   | 29 
(2 row)