IF THEN statements in SQL

[overcast]

IF TERM1_LINE='3'THEN
SELECT TERM1_LINE
FROM TERM_DATA
WHERE
TERM1_REF='TPLAN' AND
TERM1_LINE='3';
ELSE
SELECT TERM1_LINE
FROM TERM_DATA
WHERE
TERM1_REF='TPLAN' AND
TERM1_LINE='0';
END IF;

Is it possible to do something like this? (obviously not working this way) or do i have to make some kinda function or procedure?

Thanks guys