sql检查对象是否在使用中

Question

I have a table lets say tableA already filled with var_code and start_time and end_time and I want to insert a value into another table but before I insert it I want to check if this var_code is already in use in a specific time defined in tableA. To find the relation between the new object and time I had to join three tables. When I try to insert something I get an error message: ERROR: query has no destination for result data What do I do wrong?

CREATE OR REPLACE FUNCTION same_obj_does_not_already_used()
RETURNS trigger AS
$BODY$
BEGIN
declare

    var1 numeric;  
    var2 date;  
    var3 time without time zone;  
    var4 time without time zone;  
    begin
select id as var1,date as var2,start_t as var3,end_t as var4
from tableA tA inner join tableB tB 
        on (tA.id = tB.id) 
        inner join tableC tC
         on (tB.code = tC.fcode);

 if(new.id = var1 and new.date = var2 and new.start_t>=var3 and new.end_t<= var4) then
    raise exception 'Error';
end if;

 end;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION ame_obj_does_not_already_used()
OWNER TO postgres;

Answer 1

i think this part

select id as var1,date as var2,start_t as var3,end_t as var4
from tableA tA inner join tableB tB 
        on (tA.id = tB.id) 
        inner join tableC tC
         on (tB.code = tC.fcode);

should have INTO clauses..

select id, date, start_t, end_t INTO var1, var2, var3, var4