我需要验证 2 列，但有时第二列为空然后我需要验证第二列，如果它不为空，否则它只会验证第一列
SELECT *
FROM table
WHERE column1 = $_GET['id']
and column2 IS NOT NULL = $_GET['id']
这是你想要的逻辑吗？
SELECT *
FROM table
WHERE column1 = $_GET['id'] and
(column2 IS NULL or column2 = $_GET['id']);
SELECT IF(column1 IS NULL, column2, column1)
FROM table
WHERE column1 = $_GET['id'] OR column2 = $_GET['id']