How to select into a variable in PL/SQL when the result might be null?

Question

Is there a way in to just run a query once to select into a variable, considering that the query might return nothing, then in that case the variable should be null.

Answer 1

I use this syntax for flexibility and speed -

    begin
    --
    with KLUJ as
    ( select 0 ROES from dual
       union 
      select count(*) from MY_TABLE where rownum = 1
    ) select max(ROES) into has_rows from KLUJ;
    --
    end;

Dual returns 1 row, rownum adds 0 or 1 rows, and max() groups to exactly 1. This gives 0 for no rows in a table and 1 for any other number of rows.

I extend the where clause to count rows by condition, remove rownum to count rows meeting a condition, and increase rownum to count rows meeting the condition up to a limit.