SQL仅在满足条件的情况下，根据另一个列值更新Select语句列

Question

我有一个select语句，如果Task_Days_Due列task_status2值是Closed，我希望将它更新为字符串(N/A - Task is Closed)，它当前显示了到期的天数，但是如果单击，这是无关紧要的。

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以下是当前的选择：

SELECT

    Report_Run_Date,
    incident_number,
    INC_Reported_Date,
    TASK_id,
    TASK_Assigneee, 
    TASK_Status, -- Staged 1000, Assigned 2000, Pending 3000, Work In Progress 4000, Waiting 5000, Closed 6000, ByPassed 7000
    Task_Status2,
    -- Set RAG column to RAG is not closed
    case    WHEN TASK_Status = 6000  THEN "N/A - Task is Closed"
            WHEN Task_Days_Due <= 0  THEN 'Red'
            WHEN Task_Days_Due > 0 and Task_Days_Due <= 7 THEN 'Amber'
            WHEN Task_Days_Due > 7 THEN 'Green'
            WHEN Task_Days_Due is NULL THEN 'No Task End Date'
    end     as Red_Amber_Green,
    Task_Days_Due, ?????

我的挑战是，如果条件不满足，我想要保留这个值。以前的尝试是，如果列task_status2值不是Closed，则将值覆盖为null。

Answer 1

SELECT

    Report_Run_Date,
    incident_number,
    INC_Reported_Date,
    TASK_id,
    TASK_Assigneee, 
    TASK_Status, -- Staged 1000, Assigned 2000, Pending 3000, Work In Progress 4000, Waiting 5000, Closed 6000, ByPassed 7000
    Task_Status2,
    -- Set RAG column to RAG is not closed
    case    WHEN TASK_Status = 6000  THEN "N/A - Task is Closed"
            WHEN Task_Days_Due <= 0  THEN 'Red'
            WHEN Task_Days_Due > 0 and Task_Days_Due <= 7 THEN 'Amber'
            WHEN Task_Days_Due > 7 THEN 'Green'
            WHEN Task_Days_Due is NULL THEN 'No Task End Date'
    end     as Red_Amber_Green,
    decode(task_status2, 'Closed', 'N/A - Task is Closed', cast(task_days_due as STRING)) as task_days_due