write a query that returns one row. you can do this by running the query in SQLPlus without the into part of the query and see how many rows are returned. You can also add the distinct word to the clause.
generally that error occurs due to the select statement returns more than one value.
means if u issue SELECT INTO from
so every variable can hold only one value at a time.
so that if that select statment returns more than one value, then system doesn't understood which value should be stored in that variable.
thats why the error occured.
so u can try that using
SELECT DISTINCT INTO from