Oracle: Get a query to always return exactly one row, even when there's no data to be found

Question

I have a query like this:

   select data_name
   into v_name
   from data_table
   where data_table.type = v_t_id

Normally, this query shou

Answer 1

Here is my simple solution using LEFT OUTER JOIN:

CREATE TABLE data_table(data_name VARCHAR2(20), data_type NUMBER(2));

INSERT INTO data_table(data_name, data_type) VALUES('fifty-one', 51);

SELECT coalesce(data_name, 'unknown')
  FROM dual
  LEFT OUTER JOIN (SELECT data_name FROM data_table WHERE data_type = 53) o
    ON 1 = 1;

SELECT coalesce(data_name, 'unknown')
  FROM dual
  LEFT OUTER JOIN (SELECT data_name FROM data_table WHERE data_type = 51) o
    ON 1 = 1;