错误1241（21000）：操作数应包含1列：UBUNTU

Question

我正在尝试运行以下SQL查询：

SELECT DISTINCT A.date 
FROM VALUE A, BUYnSELL B 
WHERE A.currency = B.currency AND A.currency = 'ETH' AND A.exchange = 
'Coinbase' AND (B.value * B.num_of_coins) > (SELECT MAX(D.value * D.num_of_coins) FROM VALUE C, BUYnSELL D WHERE C.currency = D.currency AND C.currency = 'ETH' AND C.exchange = 'Huobi');

我觉得这应该可以工作，但是我不断出错：

ERROR 1241 (21000): Operand should contain 1 column(s)