function - postgresql check session config setting availability -

i have sensor data table full of 'holes', data saved when changes on specified threshold.

| time stamp | value1 | value2 | | 2012-01-01 | 1      |        | | 2012-01-02 |        | 2      | | 2012-01-05 |        |        | | 2012-01-20 |        |        | | 2012-03-01 | 3      | 1      | 

i need cross row calculations, holes in tables make impractical. solution create auxiliary function wrap related field, , use session parameter persistent variable. sth this:

create function wrap_data( data1 numeric(3,1) )  ... language plpgsql if data1 <> null     execute 'set session app.data1 = $1;' using data1; end if; return current_setting('app.data1')::numeric(3,1) ... 

it works before executing function, have initialized variables outside of function by:

set session app.data1 = 11.1; 

or complain parameter not unrecognized.

i looking function ifparameterexist(), allow me check existence of variable without raising error inside plpgsql function.