# Condition On WHERE Clause

oracle

I need to add a condition on the WHERE clause such that when sevnum is not null then relate the tables by premnum and sevnum. However, the code below returns an error.

SELECT *
FROM prem c, tempTable t
WHERE
CASE WHEN t.sevnum IS NOT NULL
THEN t.premnum = c.premnum
AND t.sevnum = c.sevnum
END
;


WHERE (    t.sevnum IS NOT NULL