mysql - SELECT SQL 查询 (MySQL) 中的计算列

Question

我有以下查询:

SELECT
a.source,
TotalCount,
ActiveCount
FROM
(
    SELECT COUNT(*) AS TotalCount, a.source
    FROM internship a
    GROUP BY a.source
) AS A
join
(
    SELECT COUNT(*) AS ActiveCount, b.source
    FROM internship b
    WHERE b.int_lastdate > CURDATE() AND b.status LIKE 'Published'
    GROUP BY b.source
) AS B
    ON A.source = B.source

上面的查询给了我这样的结果:

我想在此处添加另一列“ExpiredCount = TotalCount - ActiveCount”

我怎样才能做到这一点？

Answer 1

Gordon 的回答可能是我作为 DBA 继承别人代码所希望看到的。但我们实际上完全可以避免使用子查询，只需编写以下内容:

SELECT
    source,
    COUNT(*) AS TotalCount,
    SUM(CASE WHEN int_lastdate > CURDATE() AND status LIKE 'Published'
             THEN 1 ELSE 0 END) AS ActiveCount,
    COUNT(*) - SUM(CASE WHEN int_lastdate > CURDATE() AND status LIKE 'Published'
                        THEN 1 ELSE 0 END) AS ExpiredCount
FROM internship
GROUP BY source