如何从该语句中的SELECT语句中减去两个结果？

Question

这会拉回昨天和今天的两个int值。我想从名为差异的第三列中的语句中减去两个结果：

SELECT (
 SELECT COUNT(*)
 FROM collectors_users 
 WHERE DATE(dateadded) = CURDATE() - INTERVAL 1 DAY
) AS yesterday, COUNT(*) AS today 
FROM collectors_users 
WHERE DATE(dateadded) = CURDATE()

Answer 1

您需要重复表达式。 SQL（通常）不允许您在同一SELECT中重用列别名。您可以将逻辑简化为：

SELECT SUM(DATE(dateadded) = CURDATE() - INTERVAL 1 DAY) AS yesterday,
       SUM(DATE(dateadded) = CURDATE()) as today,
       (SUM(DATE(dateadded) = CURDATE()) - 
        SUM(DATE(dateadded) = CURDATE() - INTERVAL 1 DAY)
       ) as diff
FROM collectors_users
WHERE dateadded >= CURDATE() - INTERVAL 1 DAY AND
      dateadded < CURDATE() + INTERVAL 1 DAY;

请注意WHERE子句的逻辑涵盖两天。此外，它不使用DATE()。这将允许查询使用索引（如果可用）。