SQL 根据另一个 Columns 值更新 Select Statement 列，但前提是满足条件

Question

如果列task_status2的值为Closed ，我有一个 select 语句，并希望将Task_Days_Due更新为字符串（ N/A - Task is Closed ）当前它显示到期前的天数，但如果关闭则无关紧要。

这是当前的选择：

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, ?????

我的挑战是如果不满足条件，我想保持原样。 如果列task_status2值未Closed ，则先前的尝试将值覆盖为 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