mysql - 如何在查询中重用派生值

Question

必须有一种更有效的方法来做到这一点，但我对 mySQL 还不够熟悉，还不知道要研究哪些术语。我一直在研究 AS 关键字。

下面是我的工作查询。看看我如何必须多次导出持续时间 (TIME_TO_SEC(TIMEDIFF( FinishTime,StartTime))。是否可以导出一次并在此查询中重用它？

table: AuraUsers
fields: ID, StartTime, FinishTime, Completed


SELECT 
    TIME_TO_SEC(
        TIMEDIFF(
            FinishTime,
            StartTime
        )
    ) 
    AS json 
    FROM AuraUsers 
    WHERE (
        StartTime IS NOT NULL 
        AND 
        FinishTime IS NOT NULL 
        AND 
        Completed=7 
        AND 
        TIME_TO_SEC(
            TIMEDIFF(
                FinishTime,
                StartTime
            )
        ) > 0 
        AND 
        TIME_TO_SEC(
            TIMEDIFF(
                FinishTime,
                StartTime
            )
        ) < 90275
    ) 
    ORDER BY TIME_TO_SEC(
        TIMEDIFF(
            FinishTime,
            StartTime
        )
    ) DESC 
    LIMIT 0,535;

Answer 1

使用HAVING子句，但它实际上并没有重用，每次在查询中使用别名时它都会评估整个表达式

SELECT 
    TIME_TO_SEC(
        TIMEDIFF(
            FinishTime,
            StartTime
        )
    ) 
    AS json 
    FROM AuraUsers 
    HAVING (
        StartTime IS NOT NULL 
        AND 
        FinishTime IS NOT NULL 
        AND Completed=7 
        AND json > 0 
        AND json < 90275
    ) 
    ORDER BY json DESC 
    LIMIT 0,535;